2.XI.I. Miscellaneous, 1863-1866.—2.XI.II. Correspondence with Fritz Muller, 1865-1881.—2.XI.III. Miscellaneous, 1868-1881.
2.XI.I. MISCELLANEOUS, 1863-1866.
LETTER 658. TO D. OLIVER. Down {April, 1863}.
(658/1. The following letter illustrates the truth of Sir W. Thiselton-Dyer's remark that Darwin was never "afraid of his facts." (658/2. "Charles Darwin" (Nature Series), 1882, page 43.) The entrance of pollen-tubes into the nucellus by the chalaza, instead of through the micropyle, was first fully demonstrated by Treub in his paper "Sur les Casuarinees et leur place dans le Systeme naturel," published in the "Ann. Jard. Bot. Buitenzorg," X., 1891. Two years later Miss Benson gave an account of a similar phenomenon in certain Amentiferae ("Trans. Linn. Soc." 1888-94, page 409). This chalazogamic method of fertilisation has since been recognised in other flowering plants, but not, so far as we are aware, in the genus Primula.)
It is a shame to trouble {you}, but will you tell me whether the ovule of Primula is "anatropal," nearly as figured by Gray, page 123, "Lessons in Botany," or rather more tending to "amphitropal"? I never looked at such a point before. Why I am curious to know is because I put pollen into the ovarium of monstrous primroses, and now, after sixteen days, and not before (the length of time agrees with slowness of natural impregnation), I find abundance of pollen-tubes emitted, which cling firmly to the ovules, and, I think I may confidently state, penetrate the ovule. But here is an odd thing: they never once enter at (what I suppose to be) the "orifice," but generally at the chalaza...Do you know how pollen-tubes go naturally in Primula? Do they run down walls of ovarium, and then turn up the placenta, and so debouch near the "orifices" of the ovules?
If you thought it worth while to examine ovules, I would see if there are more monstrous flowers, and put pollen into the ovarium, and send you the flowers in fourteen or fifteen days afterwards. But it is rather troublesome. I would not do it unless you cared to examine the ovules. Like a foolish and idle man, I have wasted a whole morning over them...
In two ovules there was an odd appearance, as if the outer coat of ovule at the chalaza end (if I understand the ovule) had naturally opened or withered where most of the pollen-tubes seemed to penetrate, which made me at first think this was a widely open foramen. I wonder whether the ovules could be thus fertilised?
LETTER 659. TO D. OLIVER. Down {April, 1863}.
Many thanks about the Primula. I see that I was pretty right about the ovules. I have been thinking that the apparent opening at the chalaza end must have been withering or perhaps gnawing by some very minute insects, as the ovarium is open at the upper end. If I have time I will have another look at pollen-tubes, as, from what you say, they ought to find their way to the micropyle. But ovules to me are far more troublesome to dissect than animal tissue; they are so soft, and muddy the water.
LETTER 660. TO MAXWELL MASTERS. Down, April 6th {1863}.
I have been very glad to read your paper on Peloria. (660/1. "On the Existence of Two Forms of Peloria." "Natural History Review," April, 1863, page 258.) For the mere chance of the following case being new I send it. A plant which I purchased as Corydalis tuberosa has, as you know, one nectary—short, white, and without nectar; the pistil is bowed towards the true nectary; and the hood formed by the inner petals slips off towards the opposite side (all adaptations to insect agency, like many other pretty ones in this family). Now on my plants there are several flowers (the fertility of which I will observe) with both nectaries equal and purple and secreting nectar; the pistil is straight, and the hood slips off either way. In short, these flowers have the exact structure of Dielytra and Adlumia. Seeing this, I must look at the case as one of reversion; though it is one of the spreading of irregularity to two sides.
As columbine {Aquilegia} has all petals, etc., irregular, and as monkshood {Aconitum} has two petals irregular, may not the case given by Seringe, and referred to {by} you (660/2. "Seringe describes and figures a flower {of Aconitum} wherein all the sepals were helmet-shaped," and the petals similarly affected. Maxwell Masters, op. cit., page 260.), by you be looked at as reversion to the columbine state? Would it be too bold to suppose that some ancient Linaria, or allied form, and some ancient Viola, had all petals spur-shaped, and that all cases of "irregular peloria" in these genera are reversions to such imaginary ancient form? (660/3. "'Regular or Congenital Peloria' would include those flowers which, contrary to their usual habit, retain throughout the whole of their growth their primordial regularity of form and equality of proportion. 'Irregular or Acquired Peloria,' on the other hand, would include those flowers in which the irregularity of growth that ordinarily characterises some portions of the corolla is manifested in all of them." Maxwell Masters, loc. cit.)
It seems to me, in my ignorance, that it would be advantageous to consider the two forms of Peloria WHEN OCCURRING IN THE VERY SAME SPECIES as probably due to the same general law—viz., one as reversion to very early state, and the other as reversion to a later state when all the petals were irregularly formed. This seems at least to me a priori a more probable view than to look at one form of Peloria as due to reversion and the other as something distinct. (660/4. See Maxwell Masters, "Vegetable Teratology," 1869, page 235; "Variation of Animals and Plants," Edition II., Volume II., page 33.)
What do you think of this notion?
LETTER 661. TO P.H. GOSSE.
(661/1. The following was written in reply to Mr. Gosse's letter of May 30th asking for a solution of his difficulties in fertilising Stanhopea. It is reprinted by the kind permission of Mr. Edmund Gosse from his delightful book, the "Life of Philip Henry Gosse," London, 1890, page 299.)
Down, June 2nd, 1863.
It would give me real pleasure to resolve your doubts, but I cannot. I can give only suspicions and my grounds for them. I should think the non-viscidity of the stigmatic hollow was due to the plant not living under its natural conditions. Please see what I have said on Acropera. An excellent observer, Mr. J. Scott, of the Botanical Gardens, Edinburgh, finds all that I say accurate, but, nothing daunted, he with the knife enlarged the orifice and forced in pollen-masses; or he simply stuck them into the contracted orifice without coming into contact with the stigmatic surface, which is hardly at all viscid, when, lo and behold, pollen-tubes were emitted and fine seed capsules obtained. This was effected with Acropera Loddigesii; but I have no doubt that I have blundered badly about A. luteola. I mention all this because, as Mr. Scott remarks, as the plant is in our hot-houses, it is quite incredible it ever could be fertilised in its native land. The whole case is an utter enigma to me. Probably you are aware that there are cases (and it is one of the oddest facts in Physiology) of plants which, under culture, have their sexual functions in so strange a condition, that though their pollen and ovules are in a sound state and can fertilise and be fertilised by distinct but allied species, they cannot fertilise themselves. Now, Mr. Scott has found this the case with certain orchids, which again shows sexual disturbance. He had read a paper at the Botanical Society of Edinburgh, and I daresay an abstract which I have seen will appear in the "Gardeners' Chronicle"; but blunders have crept in in copying, and parts are barely intelligible. How insects act with your Stanhopea I will not pretend to conjecture. In many cases I believe the acutest man could not conjecture without seeing the insect at work. I could name common English plants in this predicament. But the musk-orchis {Herminium monorchis} is a case in point. Since publishing, my son and myself have watched the plant and seen the pollinia removed, and where do you think they invariably adhere in dozens of specimens?—always to the joint of the femur with the trochanter of the first pair of legs, and nowhere else. When one sees such adaptation as this, it would be hopeless to conjecture on the Stanhopea till we know what insect visits it. I have fully proved that my strong suspicion was correct that with many of our English orchids no nectar is excreted, but that insects penetrate the tissues for it. So I expect it must be with many foreign species. I forgot to say that if you find that you cannot fertilise any of your exotics, take pollen from some allied form, and it is quite probable that will succeed. Will you have the kindness to look occasionally at your bee-Ophrys near Torquay, and see whether pollinia are ever removed? It is my greatest puzzle. Please read what I have said on it, and on O. arachnites. I have since proved that the account of the latter is correct. I wish I could have given you better information.
P.S.—If the Flowers of the Stanhopea are not too old, remove pollen-masses from their pedicels, and stick them with a little liquid pure gum to the stigmatic cavity. After the case of the Acropera, no one can dare positively say that they would not act.
LETTER 662. TO J.D. HOOKER. Down, Saturday, 5th {December 1863}.
I am very glad that this will reach you at Kew. You will then get rest, and I do hope some lull in anxiety and fear. Nothing is so dreadful in this life as fear; it still sickens me when I cannot help remembering some of the many illnesses our children have endured. My father, who was a sceptical man, was convinced that he had distinctly traced several cases of scarlet fever to handling letters from convalescents.
The vases (662/1. Probably Wedgwood ware.) did come from my sister Susan. She is recovering, and was much pleased to hear that you liked them; I have now sent one of your notes to her, in which you speak of them as "enchanting," etc. I have had a bad spell—vomiting, every day for eleven days, and some days many times after every meal. It is astonishing the degree to which I keep up some strength. Dr. Brinton was here two days ago, and says he sees no reason {why} I may not recover my former degree of health. I should like to live to do a little more work, and often I feel sure I shall, and then again I feel that my tether is run out.
Your Hastings note, my dear old fellow, was a Copley Medal to me and more than a Copley Medal: not but what I know well that you overrate what I have been able to do. (662/2. The proposal to give the medal to Darwin failed in 1863, but his friends were successful in 1864: see "Life and Letters," III., page 28.) Now that I am disabled, I feel more than ever what a pleasure observing and making out little difficulties is. By the way, here is a very little fact which may interest you. A partridge foot is described in "Proc. Zoolog. Soc." with a huge ball of earth attached to it as hard as rock. (662/3. "Proc. Zool. Soc." 1863, page 127, by Prof. Newton, who sent the foot to Darwin: see "Origin," Edition VI., page 328.) Bird killed in 1860. Leg has been sent me, and I find it diseased, and no doubt the exudation caused earth to accumulate; now already thirty-two plants have come up from this ball of earth.
By Jove! I must write no more. Good-bye, my best of friends.
There is an Italian edition of the "Origin" preparing. This makes the fifth foreign edition—i.e. in five foreign countries. Owen will not be right in telling Longmans that the book would be utterly forgotten in ten years. Hurrah!
LETTER 663. TO D. OLIVER. Down, February 17th {1864}.
Many thanks for the Epacrids, which I have kept, as they will interest me when able to look through the microscope.
Dr. Cruger has sent me the enclosed paper, with power to do what I think fit with it. He would evidently prefer it to appear in the "Nat. Hist. Review." Please read it, and let me have your decision pretty soon. Some germanisms must be corrected; whether woodcuts are necessary I have not been able to pay attention enough to decide. If you refuse, please send it to the Linnean Society as communicated by me. (663/1. H. Cruger's "A Few Notes on the Fecundation of Orchids, etc." {Read March, 1864.} "Linn. Soc. Journ." VIII., 1864-5, page 127.) The paper has interested me extremely, and I shall have no peace till I have a good boast. The sexes are separate in Catasetum, which is a wonderful relief to me, as I have had two or three letters saying that the male C. tridentatum seeds. (663/2. See footnote Letter 608 on the sexual relation between the three forms known as Catasetum tridentatum, Monacanthus viridis, and Myanthus barbatus. For further details see Darwin, "Linn. Soc. Journ." VI., 1862, page 151, and "Fertilisation of Orchids," Edition II., page 196.) It is pretty clear to me that two or three forms are confounded under this name. Observe how curiously nearly perfect the pollen of the female is, according to Cruger,—certainly more perfect than the pollen from the Guyana species described by me. I was right in the manner in which the pollen adheres to the hairy back of the humble-bee, and hence the force of the ejection of the pollina. (663/3. This view was given in "Fertilisation of Orchids," Edition I., 1862, page 230.) I am still more pleased that I was right about insects gnawing the fleshy labellum. This is important, as it explains all the astounding projections on the labellum of Oncidium, Phalaenopsis, etc.
Excuse all my boasting. It is the best medicine for my stomach. Tell me whether you mean to take up orchids, as Hooker said you were thinking of doing. Do you know Coryanthes, with its wonderful basket of water? See what Cruger says about it. It beats everything in orchids. (663/4. For Coryanthes see "Fertilisation of Orchids," Edition II., page 173.)
LETTER 664. TO J.D. HOOKER. Down {September 13th, 1864}.
Thanks for your note of the 5th. You think much and greatly too much of me and my doings; but this is pleasant, for you have represented for many years the whole great public to me.
I have read with interest Bentham's address on hybridism. I am glad that he is cautious about Naudin's view, for I cannot think that it will hold. (664/1. C. Naudin's "Nouvelles Recherches sur l'Hydridite dans les Vegetaux." The complete paper, with coloured plates, was presented to the Academy in 1861, and published in full in the "Nouvelles Archives de Museum d'Hist. Nat." Volume I., 1865, page 25. The second part only appeared in the "Ann. Sci. Nat." XIX., 1863. Mr. Bentham's address dealing with hybridism is in "Proc. Linn. Soc." VIII., 1864, page ix. A review of Naudin is given in the "Natural History Review," 1864, page 50. Naudin's paper is of much interest, as containing a mechanical theory of reproduction of the same general character as that of pangenesis. In the "Variation of Animals and Plants," Edition II., Volume II., page 395, Darwin states that in his treatment of hybridism in terms of gemmules he is practically following Naudin's treatment of the same theme in terms of "essences." Naudin, however, does not clearly distinguish between hybrid and pure gemmules, and makes the assumption that the hybrid or mixed essences tend constantly to dissociate into pure parental essences, and thus lead to reversion. It is to this view that Darwin refers when he says that Naudin's view throws no light on the reversion to long-lost characters. His own attempt at explaining this fact occurs in "Variation under Domestication," II., Edition II., page 395. Mr. Bateson ("Mendel's Principle of Heredity," Cambridge, 1902, page 38) says: "Naudin clearly enuntiated what we shall henceforth know as the Mendelian conception of the dissociation of characters of cross-breds in the formation of the germ-cells, though apparently he never developed this conception." It is remarkable that, as far as we know, Darwin never in any way came across Mendel's work. One of Darwin's correspondents, however, the late Mr. T. Laxton, of Stamford, was close on the trail of Mendelian principle. Mr. Bateson writes (op. cit., page 181): "Had he {Laxton} with his other gifts combined this penetration which detects a great principle hidden in the thin mist of 'exceptions,' we should have been able to claim for him that honour which must ever be Mendel's in the history of discovery.") The tendency of hybrids to revert to either parent is part of a wider law (which I am fully convinced that I can show experimentally), namely, that crossing races as well as species tends to bring back characters which existed in progenitors hundreds and thousands of generations ago. Why this should be so, God knows. But Naudin's view throws no light, that I can see, on this reversion of long-lost characters. I wish the Ray Society would translate Gartner's "Bastarderzeugung"; it contains more valuable matter than all other writers put together, and would do great service if better known. (664/2. "Versuche uber die Bastarderzeugung im Pflanzenreich": Stuttgart, 1849.)
LETTER 665. TO T.H. HUXLEY.
(665/1. Mr. Huxley had doubted the accuracy of observations on Catasetum published in the "Fertilisation of Orchids." In what formed the postscript to the following letter, Darwin wrote: "I have had more Catasetums,—all right, you audacious 'caviller.'")
Down, October 31st {1862}.
In a little book, just published, called the "Three Barriers" (a theological hash of old abuse of me), Owen gives to the author a new resume of his brain doctrine; and I thought you would like to hear of this. He ends with a delightful sentence. "No science affords more scope or easier ground for the caviller and controversialist; and these do good by preventing scholars from giving more force to generalisations than the master propounding them does, or meant his readers or hearers to give."
You will blush with pleasure to hear that you are of some use to the master.
LETTER 666. TO J.D. HOOKER. {February, 1864?}
I shall write again. I write now merely to ask, if you have Naravelia (666/1. Ranunculaceae.) (the Clematis-like plant told me by Oliver), to try and propagate me a plant at once. Have you Clematis cirrhosa? It will amuse me to tell you why Clematis interests me, and why I should so very much like to have Naravelia. The leaves of Clematis have no spontaneous movement, nor have the internodes; but when by growth the peduncles of leaves are brought into contact with any object, they bend and catch hold. The slightest stimulus suffices, even a bit of cotton thread a few inches long; but the stimulus must be applied during six or twelve hours, and when the peduncles once bend, though the touching object be removed, they never get straight again. Now mark the difference in another leaf-climber—viz., Tropaeolum: here the young internodes revolve day and night, and the peduncles of the leaves are thus brought into contact with an object, and the slightest momentary touch causes them to bend in any direction and catch the object, but as the axis revolves they must be often dragged away without catching, and then the peduncles straighten themselves again, and are again ready to catch. So that the nervous system of Clematis feels only a prolonged touch—that of Tropaeolum a momentary touch: the peduncles of the latter recover their original position, but Clematis, as it comes into contact by growth with fixed objects, has no occasion to recover its position, and cannot do so. You did send me Flagellaria, but most unfortunately young plants do not have tendrils, and I fear my plant will not get them for another year, and this I much regret, as these leaf-tendrils seem very curious, and in Gloriosa I could not make out the action, but I have now a young plant of Gloriosa growing up (as yet with simple leaves) which I hope to make out. Thank Oliver for decisive answer about tendrils of vines. It is very strange that tendrils formed of modified leaves and branches should agree in all their four highly remarkable properties. I can show a beautiful gradation by which LEAVES produce tendrils, but how the axis passes into a tendril utterly puzzles me. I would give a guinea if vine-tednrils could be found to be leaves.
(666/2. It is an interesting fact that Darwin's work on climbing plants was well advanced before he discovered the existence of the works of Palm, Mohl, and Dutrochet on this subject. On March 22nd, 1864, he wrote to Hooker:—"You quite overrate my tendril work, and there is no occasion to plague myself about priority." In June he speaks of having read "two German books, and all, I believe, that has been written on climbers, and it has stirred me up to find that I have a good deal of new matter.")
LETTER 667. TO J.D. HOOKER. Down, June 2nd {1864}.
You once offered me a Combretum. (667/1. The two forms of shoot in C. argenteum are described in "Climbing Plants," page 41.) I having C. purpureum, out of modesty like an ass refused. Can you now send me a plant? I have a sudden access of furor about climbers. Do you grow Adlumia cirrhosa? Your seed did not germinate with me. Could you have a seedling dug up and potted? I want it fearfully, for it is a leaf-climber, and therefore sacred.
I have some hopes of getting Adlumia, for I used to grow the plant, and seedlings have often come up, and we are now potting all minute reddish-coloured weeds. (667/2. We believe that the Adlumia which came up year by year in flower boxes in the Down verandah grew from seed supplied by Asa Gray.) I have just got a plant with sensitive axis, quite a new case; and tell Oliver I now do not care at all how many tendrils he makes axial, which at one time was a cruel torture to me.
LETTER 668. TO J.D. HOOKER. Down, November 3rd {1864}.
Many thanks for your splendid long letter. But first for business. Please look carefully at the enclosed specimen of Dicentra thalictriformis, and throw away. (668/1. Dicentra thalictrifolia, a Himalayan species of Fumariaceae, with leaf-tendrils.) When the plant was young I concluded certainly that the tendrils were axial, or modified branches, which Mohl says is the case with some Fumariaceae. (668/2. "Ueber den Bau und das Winden der Ranken und Schlingpflanzen. Eine gekronte Preisschrift," 4to, Tubingen, 1827. At page 43 Mohl describes the tips of the branches of Fumaria {Corydalis} clavicualta as being developed into tendrils, as well as the leaves. For this reason Darwin placed the plant among the tendril-bearers rather than among the true leaf-climbers: see "Climbing Plants," Edition II., 1875, page 121.) You looked at them here and agreed. But now the plant is old, what I thought was a branch with two leaves and ending in a tendril looks like a gigantic leaf with two compound leaflets, and the terminal part converted into a tendril. For I see buds in the fork between supposed branch and main stem. Pray look carefully—you know I am profoundly ignorant—and save me from a horrid mistake.
LETTER 669. TO J.D. HOOKER.
(669/1. The following is interesting, as containing a foreshadowing of the chemotaxis of antherozoids which was shown to exist by Pfeffer in 1881: see "Untersuchungen aus dem botanischen Institut zu Tubingen," Volume I., page 363. There are several papers by H.J. Carter on the reproduction of the lower organisms in the "Annals and Magazine of Natural History" between 1855 and 1865.)
Down, Sunday, 22nd, and Saturday, 28th {October, 1865}.
I have been wading through the "Annals and Mag. of N. History." for last ten years, and have been interested by several papers, chiefly, however, translations; but none have interested me more than Carter's on lower vegetables, infusoria, and protozoa. Is he as good a workman as he appears? for if so he would deserve a Royal medal. I know it is not new; but how wonderful his account of the spermatozoa of some dioecious alga or conferva, swimming and finding the minute micropyle in a distinct plant, and forcing its way in! Why, these zoospores must possess some sort of organ of sense to guide their locomotive powers to the small micropyle; and does not this necessarily imply something like a nervous system, in the same way as complemental male cirripedes have organs of sense and locomotion, and nothing else but a sack of spermatozoa?
LETTER 670. TO F. HILDEBRAND. May 16th, 1866.
Since writing to you before, I have read your admirable memoir on Salvia (670/1. "Pringsheim's Jahrbucher," Volume IV., 1866.), and it has interested me almost as much as when I first investigated the structure of orchids. Your paper illustrates several points in my "Origin of Species," especially the transition of organs. Knowing only two or three species in the genus, I had often marvelled how one cell of the anther could have been transformed into the moveable plate or spoon; and how well you show the gradations. But I am surprised that you did not more strongly insist on this point.
I shall be still more surprised if you do not ultimately come to the same belief with me, as shown by so many beautiful contrivances,—that all plants require, from some unknown cause, to be occasionally fertilised by pollen from a distinct individual.
(PLATE: FRITZ MULLER.) 2.XI.II. CORRESPONDENCE WITH FRITZ MULLER, 1865-1881.
(671/1. The letters from Darwin to Muller are given as a separate group, instead of in chronological sequence with the other botanical letters, as better illustrating the uninterrupted friendship and scientific comradeship of the two naturalists.)
LETTER 671. TO F. MULLER. Down, October 17th {1865}.
I received about a fortnight ago your second letter on climbing plants, dated August 31st. It has greatly interested me, and it corrects and fills up a great hiatus in my paper. As I thought you could not object, I am having your letter copied, and will send the paper to the Linnean Society. (671/2. "Notes on some of the Climbing Plants near Desterro" {1865}, "Linn. Soc. Journ." IX., 1867.) I have slightly modified the arrangement of some parts and altered only a few words, as you write as good English as an Englishman. I do not quite understand your account of the arrangement of the leaves of Strychnos, and I think you use the word "bracteae" differently to what English authors do; therefore I will get Dr. Hooker to look over your paper.
I cannot, of course, say whether the Linnean Society will publish your paper; but I am sure it ought to do so. As the Society is rather poor, I fear that it will give only a few woodcuts from your truly admirable sketches.
LETTER 672. TO F. MULLER.
(672/1. In Darwin's book on Climbing Plants, 1875 (672/2. First given as a paper before the Linnean Society, and published in the "Linn. Soc. Journ." Volume IX.,), he wrote (page 205): "The conclusion is forced on our minds that the capacity of revolving, on which most climbing plants depend, is inherent, though undeveloped, in almost every plant in the vegetable Kingdom"—a conclusion which was verified in the "Power of Movement in Plants." The present letter is interesting in referring to Fritz Muller's observations on the "revolving nutation," or circumnutation of Alisma macrophylla and Linum usitatissimum, the latter fact having been discovered by F. Muller's daughter Rosa. This was probably the earliest observation on the circumnutation of a non-climbing plant, and Muller, in a paper dated 1868, and published in Volume V. of the "Jenaische Zeitschrift," page 133, calls attention to its importance in relation to the evolution of the habit of climbing. The present letter was probably written in 1865, since it refers to Muller's paper read before the Linnean Soc. on December 7th, 1865. If so, the facts on circumnutation must have been communicated to Darwin some years before their publication in the "Jenaische Zeitschrift.")
Down, December 9th {1865}.
I have received your interesting letter of October 10th, with its new facts on branch-tendrils. If the Linnean Society publishes your paper (672/3. Ibid., 1867, page 344.), as I am sure it ought to do, I will append a note with some of these new facts.
I forwarded immediately your MS. to Professor Max Schultze, but I did not read it, for German handwriting utterly puzzles me, and I am so weak, I am capable of no exertion. I took the liberty, however, of asking him to send me a copy, if separate ones are printed, and I reminded him about the Sponge paper.
You will have received before this my book on orchids, and I wish I had known that you would have preferred the English edition. Should the German edition fail to reach you, I will send an English one. That is a curious observation of your daughter about the movement of the apex of the stem of Linum, and would, I think, be worth following out. (672/4. F. Muller, "Jenaische Zeitschrift," Bd. V., page 137. Here, also, are described the movements of Alisma.) I suspect many plants move a little, following the sun; but all do not, for I have watched some pretty carefully.
I can give you no zoological news, for I live the life of the most secluded hermit.
I occasionally hear from Ernest Hackel, who seems as determined as you are to work out the subject of the change of species. You will have seen his curious paper on certain medusae reproducing themselves by seminal generation at two periods of growth.
(672/5. On April 3rd, 1868, Darwin wrote to F. Muller: "Your diagram of the movements of the flower-peduncle of the Alisma is extremely curious. I suppose the movement is of no service to the plant, but shows how easily the species might be converted into a climber. Does it bend through irritability when rubbed?"
LETTER 673. TO F. MULLER. Down, September 25th {1866}.
I have just received your letter of August 2nd, and am, as usual, astonished at the number of interesting points which you observe. It is quite curious how, by coincidence, you have been observing the same subjects that have lately interested me.
Your case of the Notylia is quite new to me (673/1. See F. Muller, "Bot. Zeitung," 1868, page 630; "Fertilisation of Orchids," Edition II., page 171.); but it seems analogous with that of Acropera, about the sexes of which I blundered greatly in my book. I have got an Acropera now in flower, and have no doubt that some insect, with a tuft of hairs on its tail, removes by the tuft, the pollinia, and inserts the little viscid cap and the long pedicel into the narrow stigmatic cavity, and leaves it there with the pollen-masses in close contact with, but not inserted into, the stigmatic cavity. I find I can thus fertilise the flowers, and so I can with Stanhopea, and I suspect that this is the case with your Notylia. But I have lately had an orchis in flower—viz. Acineta, which I could not anyhow fertilise. Dr. Hildebrand lately wrote a paper (673/2. "Bot. Zeitung," 1863, 1865.) showing that with some orchids the ovules are not mature and are not fertilised until months after the pollen-tubes have penetrated the column, and you have independently observed the same fact, which I never suspected in the case of Acropera. The column of such orchids must act almost like the spermatheca of insects. Your orchis with two leaf-like stigmas is new to me; but I feel guilty at your wasting your valuable time in making such beautiful drawings for my amusement.
Your observations on those plants being sterile which grow separately, or flower earlier than others, are very interesting to me: they would be worth experimenting on with other individuals. I shall give in my next book several cases of individual plants being sterile with their own pollen. I have actually got on my list Eschscholtzia (673/3. See "Animals and Plants," II., Edition II., page 118.) for fertilising with its own pollen, though I did not suspect it would prove sterile, and I will try next summer. My object is to compare the rate of growth of plants raised from seed fertilised by pollen from the same flower and by pollen from a distinct plant, and I think from what I have seen I shall arrive at interesting results. Dr. Hildebrand has lately described a curious case of Corydalis cava which is quite sterile with its own pollen, but fertile with pollen of any other individual plant of the species. (673/4. "International Horticultural Congress," London, 1866, quoted in "Variation of Animals and Plants," Edition II., Volume II., page 113.) What I meant in my paper on Linum about plants being dimorphic in function alone, was that they should be divided into two equal bodies functionally but not structurally different. I have been much interested by what you say on seeds which adhere to the valves being rendered conspicuous. You will see in the new edition of the "Origin" (673/5. "Origin of Species," Edition IV., 1866, page 238. A discussion on the origin of beauty, including the bright colours of flowers and fruits.) why I have alluded to the beauty and bright colours of fruit; after writing this it troubled me that I remembered to have seen brilliantly coloured seed, and your view occurred to me. There is a species of peony in which the inside of the pod is crimson and the seeds dark purple. I had asked a friend to send me some of these seeds, to see if they were covered with anything which could prove attractive to birds. I received some seeds the day after receiving your letter, and I must own that the fleshy covering is so thin that I can hardly believe it would lead birds to devour them; and so it was in an analogous case with Passiflora gracilis. How is this in the cases mentioned by you? The whole case seems to me rather a striking one.
I wish I had heard of Mikania being a leaf-climber before your paper was printed (673/6. See "Climbing Plants (3rd thousand, 1882), page 116. Mikania and Mutisia both belong to the Compositae. Mikania scandens is a twining plant: it is another species which, by its leaf-climbing habit, supplies a transition to the tendril-climber Mutisia. F. Muller's paper is in "Linn. Soc. Journ." IX., page 344.), for we thus get a good gradation from M. scandens to Mutisia, with its little modified, leaf-like tendrils.
I am glad to hear that you can confirm (but render still more wonderful) Hackel's most interesting case of Linope. Huxley told me that he thought the case would somehow be explained away.
LETTER 674. TO F. MULLER. Down {Received January 24th, 1867}.
I have so much to thank you for that I hardly know how to begin. I have received the bulbils of Oxalis, and your most interesting letter of October 1st. I planted half the bulbs, and will plant the other half in the spring. The case seems to me very curious, and until trying some experiments in crossing I can form no conjecture what the abortion of the stamens in so irregular a manner can signify. But I fear from what you say the plant will prove sterile, like so many others which increase largely by buds of various kinds. Since I asked you about Oxalis, Dr. Hildebrand has published a paper showing that a great number of species are trimorphic, like Lythrum, but he has tried hardly any experiments. (674/1. Hildebrand's work, published in the "Monatsb. d. Akad. d. Wiss. Berlin," 1866, was chiefly on herbarium specimens. His experimental work was published in the "Bot. Zeitung," 1871.)
I am particularly obliged for the information and specimens of Cordia (674/2. Cordiaceae: probably dimorphic.), and shall be most grateful for seed. I have not heard of any dimorphic species in this family. Hardly anything in your letter interested me so much as your account and drawing of the valves of the pod of one of the Mimoseae with the really beautiful seeds. I will send some of these seeds to Kew to be planted. But these seeds seem to me to offer a very great difficulty. They do not seem hard enough to resist the triturating power of the gizzard of a gallinaceous bird, though they must resist that of some other birds; for the skin is as hard as ivory. I presume that these seeds cannot be covered with any attractive pulp? I soaked one of the seeds for ten hours in warm water, which became only very slightly mucilaginous. I think I will try whether they will pass through a fowl uninjured. (674/3. The seeds proved to be those of Adenanthera pavonina. The solution of the difficulty is given in the following extract from a letter to Muller, March 2nd, 1867: "I wrote to India on the subject, and I hear from Mr. J. Scott that parrots are eager for the seeds, and, wonderful as the fact is, can split them open with their beaks; they first collect a large number in their beaks, and then settle themselves to split them, and in doing so drop many; thus I have no doubt they are disseminated, on the same principle that the acorns of our oaks are most widely disseminated." Possibly a similar explanation may hold good for the brightly coloured seeds of Abrus precatorius.) I hope you will observe whether any bird devours them; and could you get any young man to shoot some and observe whether the seeds are found low down in the intestines? It would be well worth while to plant such seeds with undigested seeds for comparison. An opponent of ours might make a capital case against us by saying that here beautiful pods and seeds have been formed not for the good of the plant, but for the good of birds alone. These seeds would make a beautiful bracelet for one of my daughters, if I had enough. I may just mention that Euonymus europoeus is a case in point: the seeds are coated by a thin orange layer, which I find is sufficient to cause them to be devoured by birds.
I have received your paper on Martha {Posoqueria (674/4. "Bot. Zeitung," 1866.)}; it is as wonderful as the most wonderful orchis; Ernst Hackel brought me the paper and stayed a day with me. I have seldom seen a more pleasant, cordial, and frank man. He is now in Madeira, where he is going to work chiefly on the Medusae. His great work is now published, and I have a copy; but the german is so difficult I can make out but little of it, and I fear it is too large a work to be translated. Your fact about the number of seeds in the capsule of the Maxillaria (674/5. See "Animals and Plants," Edition II., Volume II., page 115.) came just at the right time, as I wished to give one or two such facts. Does this orchid produce many capsules? I cannot answer your question about the aerial roots of Catasetum. I hope you have received the new edition of the "Origin." Your paper on climbing plants (674/6. "Linn. Soc. Journal," IX., 1867, page 344.) is printed, and I expect in a day or two to receive the spare copies, and I will send off three copies as before stated, and will retain some in case you should wish me to send them to any one in Europe, and will transmit the remainder to yourself.
LETTER 675. TO F. MULLER. Down {received February 24th, 1867}.
Your letter of November 2nd contained an extraordinary amount of interesting matter. What a number of dimorphic plants South Brazil produces: you observed in one day as many or more dimorphic genera than all the botanists in Europe have ever observed. When my present book is finished I shall write a final paper upon these plants, so that I am extremely glad to hear of your observations and to see the dried flowers; nevertheless, I should regret MUCH if I prevented you from publishing on the subject. Plumbago (675/1. Plumbago has not been shown to be dimorphic.) is quite new to me, though I had suspected it. It is curious how dimorphism prevails by groups throughout the world, showing, as I suppose, that it is an ancient character; thus Hedyotis is dimorphic in India (675/2. Hedyotis was sent to Darwin by F. Muller; it seems possible, therefore, that Hedyotis was written by mistake for some other Rubiaceous plant, perhaps Oldenlandia, which John Scott sent him from India.); the two other genera in the same sub-family with Villarsia are dimorphic in Europe and Ceylon; a sub-genus of Erythroxylon (675/3. No doubt Sethia.) is dimorphic in Ceylon, and Oxalis with you and at the Cape of Good Hope. If you can find a dimorphic Oxalis it will be a new point, for all known species are trimorphic or monomorphic. The case of Convolvulus will be new, if proved. I am doubtful about Gesneria (675/4. Neither Convolvulus nor Gesneria have been shown to be dimorphic.), and have been often myself deceived by varying length of pistil. A difference in the size of the pollen-grains would be conclusive evidence; but in some cases experiments by fertilisation can alone decide the point. As yet I know of no case of dimorphism in flowers which are very irregular; such flowers being apparently always sufficiently visited and crossed by insects.
LETTER 676. TO F. MULLER. Down, April 22nd {1867}.
I am very sorry your papers on climbing plants never reached you. They must be lost, but I put the stamps on myself and I am sure they were right. I despatched on the 20th all the remaining copies, except one for myself. Your letter of March 4th contained much interesting matter, but I have to say this of all your letters. I am particularly glad to hear that Oncidium flexuosum (676/1. See "Animals and Plants," Edition II., Volume II., page 114. Observations on Oncidium were made by John Scott, and in Brazil by F. Muller, who "fertilised above one hundred flowers of the above-mentioned Oncidium flexuosum, which is there endemic, with its own pollen, and with that taken from distinct plants: all the former were sterile, whilst those fertilised by pollen from any OTHER PLANT of the same species were fertile.') is endemic, for I always thought that the cases of self-sterility with orchids in hot-houses might have been caused by their unnatural conditions. I am glad, also, to hear of the other analogous cases, all of which I will give briefly in my book that is now printing. The lessened number of good seeds in the self-fertilising Epidendrums is to a certain extent a new case. You suggest the comparison of the growth of plants produced from self-fertilised and crossed seeds. I began this work last autumn, and the result, in some cases, has been very striking; but only, as far as I can yet judge, with exotic plants which do not get freely crossed by insects in this country. In some of these cases it is really a wonderful physiological fact to see the difference of growth in the plants produced from self-fertilised and crossed seeds, both produced by the same parent-plant; the pollen which has been used for the cross having been taken from a distinct plant that grew in the same flower-pot. Many thanks for the dimorphic Rubiaceous plant. Three of your Plumbagos have germinated, but not as yet any of the Lobelias. Have you ever thought of publishing a work which might contain miscellaneous observations on all branches of Natural History, with a short description of the country and of any excursions which you might take? I feel certain that you might make a very valuable and interesting book, for every one of your letters is so full of good observations. Such books, for instance Bates' "Travels on the Amazons," are very popular in England. I will give your obliging offer about Brazilian plants to Dr. Hooker, who was to have come here to-day, but has failed. He is an excellent good fellow, as well as naturalist. He has lately published a pamphlet, which I think you would like to read; and I will try and get a copy and send you. (676/2. Sir J.D. Hooker's lecture on Insular Floras, given before the British Association in August, 1866, is doubtless referred to. It appeared in the "Gardeners' Chronicle," and was published as a pamphlet in January, 1867. This fact helps to fix the date of the present letter.)
LETTER 677. TO F. MULLER.
(677/1. The following refers to the curious case of Eschscholtzia described in "Cross and Self-Fertilisation," pages 343-4. The offspring of English plants after growing for two generations in Brazil became self-sterile, while the offspring of Brazilian plants became partly self-fertile in England.)
January 30th {1868}.
...The flowers of Eschscholtzia when crossed with pollen from a distinct plant produced 91 per cent. of capsules; when self-fertilised the flowers produced only 66 per cent. of capsules. An equal number of crossed and self-fertilised capsules contained seed by weight in the proportion of 100 to 71. Nevertheless, the self-fertilised flowers produced an abundance of seed. I enclose a few crossed seeds in hopes that you will raise a plant, cover it with a net, and observe whether it is self-fertile; at the same time allowing several uncovered plants to produce capsules, for the sterility formerly observed by you seems to me very curious.
LETTER 678. TO F. MULLER. Down, November 28th {1868}.
You end your letter of September 9th by saying that it is a very dull one; indeed, you make a very great mistake, for it abounds with interesting facts and thoughts. Your account of the tameness of the birds which apparently have wandered from the interior, is very curious. But I must begin on another subject: there has been a great and very vexatious, but unavoidable delay in the publication of your book. (678/1. "Facts and Arguments for Darwin," 1869, a translation by the late Mr. Dallas of F. Muller's "Fur Darwin," 1864: see Volume I., Letter 227.) Prof. Huxley agrees with me that Mr. Dallas is by far the best translator, but he is much overworked and had not quite finished the translation about a fortnight ago. He has charge of the Museum at York, and is now trying to get the situation of Assistant Secretary at the Geological Society; and all the canvassing, etc., and his removal, if he gets the place, will, I fear, cause more than a month's delay in the completion of the translation; and this I very much regret.
I am particularly glad to hear that you intend to repeat my experiments on illegitimate offspring, for no one's observations can be trusted until repeated. You will find the work very troublesome, owing to the death of plants and accidents of all kinds. Some dimorphic plant will probably prove too sterile for you to raise offspring; and others too fertile for much sterility to be expected in their offspring. Primula is bad on account of the difficulty of deciding which seeds may be considered as good. I have earnestly wished that some one would repeat these experiments, but I feared that years would elapse before any one would take the trouble. I received your paper on Bignonia in "Bot. Zeit." and it interested me much. (678/2. See "Variation of Animals and Plants," Edition II., Volume II., page 117. Fritz Muller's paper, "Befruchtungsversuche an Cipo alho (Bignonia)," "Botanische Zeitung," September 25th, 1868, page 625, contains an interesting foreshadowing of the generalisation arrived at in "Cross and Self-Fertilisation." Muller wrote: "Are the three which grow near each other seedlings from the same mother-plant or perhaps from seeds of the same capsule? Or have they, from growing in the same place and under the same conditions, become so like each other that the pollen of one has hardly any more effect on the others than their own pollen? Or, on the contrary, were the plants originally one—i.e., are they suckers from a single stock, which have gained a slight degree of mutual fertility in the course of an independent life? Or, lastly, is the result 'ein neckische Zufall,'" (The above is a free translation of Muller's words.)) I am convinced that if you can prove that a plant growing in a distant place under different conditions is more effective in fertilisation than one growing close by, you will make a great step in the essence of sexual reproduction.
Prof. Asa Gray and Dr. Hooker have been staying here, and, oddly enough, they knew nothing of your paper on Martha (678/3. F. Muller has described ("Bot. Zeitung," 1866, page 129) the explosive mechanism by which the pollen is distributed in Martha (Posoqueria) fragrans. He also gives an account of the remarkable arrangement for ensuring cross-fertilisation. See "Forms of Flowers," Edition II., page 131.), though the former was aware of the curious movements of the stamens, but so little understood the structure of the plant that he thought it was probably a dimorphic species. Accordingly, I showed them your drawings and gave them a little lecture, and they were perfectly charmed with your account. Hildebrand (678/4. See Letter 206, Volume I.) has repeated his experiments on potatoes, and so have I, but this summer with no result.
LETTER 679. TO F. MULLER. Down, March 14th {1869}.
I received some time ago a very interesting letter from you with many facts about Oxalis, and about the non-seeding and spreading of one species. I may mention that our common O. acetosella varies much in length of pistils and stamens, so that I at first thought it was certainly dimorphic, but proved it by experiment not to be so. Boiseria (679/1. This perhaps refers to Boissiera (Ladizabala).) has after all seeded well with me when crossed by opposite form, but very sparingly when self-fertilised. Your case of Faramea astonishes me. (679/2. See "Forms of Flowers," Edition II., page 129. Faramea is placed among the dimorphic species.) Are you sure there is no mistake? The difference in size of flower and wonderful difference in size and structure of pollen-grains naturally make me rather sceptical. I never fail to admire and to be surprised at the number of points to which you attend. I go on slowly at my next book, and though I never am idle, I make but slow progress; for I am often interrupted by being unwell, and my subject of sexual selection has grown into a very large one. I have also had to correct a new edition of my "Origin," (679/3. The 5th edition.), and this has taken me six weeks, for science progresses at railroad speed. I cannot tell you how rejoiced I am that your book is at last out; for whether it sells largely or not, I am certain it will produce a great effect on all capable judges, though these are few in number.
P.S.—I have just received your letter of January 12th. I am greatly interested by what you say on Eschscholtzia; I wish your plants had succeeded better. It seems pretty clear that the species is much more self-sterile under the climate of Brazil than here, and this seems to me an important result. (679/4. See Letter 677.) I have no spare seeds at present, but will send for some from the nurseryman, which, though not so good for our purpose, will be worth trying. I can send some of my own in the autumn. You could simply cover up separately two or three single plants, and see if they will seed without aid,—mine did abundantly. Very many thanks for seeds of Oxalis: how I wish I had more strength and time to carry on these experiments, but when I write in the morning, I have hardly heart to do anything in the afternoon. Your grass is most wonderful. You ought to send account to the "Bot. Zeitung." Could you not ascertain whether the barbs are sensitive, and how soon they become spiral in the bud? Your bird is, I have no doubt, the Molothrus mentioned in my "Journal of Travels," page 52, as representing a North American species, both with cuckoo-like habits. I know that seeds from same spike transmitted to a certain extent their proper qualities; but as far as I know, no one has hitherto shown how far this holds good, and the fact is very interesting. The experiment would be well worth trying with flowers bearing different numbers of petals. Your explanation agrees beautifully with the hypothesis of pangenesis, and delights me. If you try other cases, do draw up a paper on the subject of inheritance of separate flowers for the "Bot. Zeitung" or some journal. Most men, as far as my experience goes, are too ready to publish, but you seem to enjoy making most interesting observations and discoveries, and are sadly too slow in publishing.
LETTER 680. TO F. MULLER. Barmouth, July 18th, 1869.
I received your last letter shortly before leaving home for this place. Owing to this cause and to having been more unwell than usual I have been very dilatory in writing to you. When I last heard, about six or eight weeks ago, from Mr. Murray, one hundred copies of your book had been sold, and I daresay five hundred may now be sold. (680/1. "Facts and Arguments for Darwin," 1869: see Volume I., Letter 227.) This will quite repay me, if not all the money; for I am sure that your book will have got into the hands of a good many men capable of understanding it: indeed, I know that it has. But it is too deep for the general public. I sent you two or three reviews—one of which, in the "Athenaeum," was unfavourable; but this journal has abused me, and all who think with me, for many years. (680/2. "Athenaeum," 1869, page 431.) I enclose two more notices, not that they are worth sending: some other brief notices have appeared. The case of the Abitulon sterile with some individuals is remarkable (680/3. "Bestaubungsversuche an Abutilon-Arten." "Jenaische Zeitschr." VII., 1873, page 22.): I believe that I had one plant of Reseda odorata which was fertile with own pollen, but all that I have tried since were sterile except with pollen from some other individual. I planted the seeds of the Abitulon, but I fear that they were crushed in the letter. Your Eschscholtzia plants were growing well when I left home, to which place we shall return by the end of this month, and I will observe whether they are self-sterile. I sent your curious account of the monstrous Begonia to the Linnean Society, and I suppose it will be published in the "Journal." (680/4. "On the Modification of the Stamens in a Species of Begonia." "Journ. Linn. Soc." XI., 1871, page 472.) I sent the extract about grafted orange trees to the "Gardeners' Chronicle," where it appeared. I have lately drawn up some notes for a French translation of my Orchis book: I took out your letters to make an abstract of your numerous discussions, but I found I had not strength or time to do so, and this caused me great regret. I have {in the French edition} alluded to your work, which will also be published in English, as you will see in my paper, and which I will send you. (680/5. "Notes on the Fertilisation of Orchids." "Ann. Mag. Nat. Hist." 1869, Volume IV., page 141. The paper gives an English version of the notes prepared for the French edition of the Orchid book.)
P.S.—By an odd chance, since I wrote the beginning of this letter, I have received one from Dr. Hooker, who has been reading "Fur Darwin": he finds that he has not knowledge enough for the first part; but says that Chapters X. and XI. "strike me as remarkably good." He is also particularly struck with one of your highly suggestive remarks in the note to page 119. Assuredly all who read your book will greatly profit by it, and I rejoice that it has appeared in English.
LETTER 681. TO F. MULLER. Down, December 1st {1869}.
I am much obliged for your letter of October 18th, with the curious account of Abutilon, and for the seeds. A friend of mine, Mr. Farrer, has lately been studying the fertilisation of Passiflora (681/1. See Letters 701 and 704.), and concluded from the curiously crooked passage into the nectary that it could not be fertilised by humming-birds; but that Tacsonia was thus fertilised. Therefore I sent him the passage from your letter, and I enclose a copy of his answer. If you are inclined to gratify him by making a few observations on this subject I shall be much obliged, and will send them on to him. I enclose a copy of my rough notes on your Eschscholtzia, as you might like to see them. Somebody has sent me from Germany two papers by you, one with a most curious account of Alisma (681/2. See Letter 672.), and the other on crustaceans. Your observations on the branchiae and heart have interested me extremely.
Alex. Agassiz has just paid me a visit with his wife. He has been in England two or three months, and is now going to tour over the Continent to see all the zoologists. We liked him very much. He is a great admirer of yours, and he tells me that your correspondence and book first made him believe in evolution. This must have been a great blow to his father, who, as he tells me, is very well, and so vigorous that he can work twice as long as he (the son) can.
Dr. Meyer has sent me his translation of Wallace's "Malay Archipelago," which is a valuable work; and as I have no use for the translation, I will this day forward it to you by post, but, to save postage, via England.
LETTER 682. TO F. MULLER. Down, May 12th {1870}.
I thank you for your two letters of December 15th and March 29th, both abounding with curious facts. I have been particularly glad to hear in your last about the Eschscholtzia (682/1. See Letter 677.); for I am now rearing crossed and self-fertilised plants, in antagonism to each other, from your semi-sterile plants so that I may compare this comparative growth with that of the offspring of English fertile plants. I have forwarded your postscript about Passiflora, with the seeds, to Mr. Farrer, who I am sure will be greatly obliged to you; the turning up of the pendant flower plainly indicates some adaptation. When I next go to London I will take up the specimens of butterflies, and show them to Mr. Butler, of the British Museum, who is a learned lepidopterist and interested on the subject. This reminds me to ask you whether you received my letter {asking} about the ticking butterfly, described at page 33 of my "Journal of Researches"; viz., whether the sound is in anyway sexual? Perhaps the species does not inhabit your island. (682/2. Papilio feronia, a Brazilian species capable of making "a clicking noise, similar to that produced by a toothed wheel passing under a spring catch."—"Journal," 1879, page 34.)
The case described in your last letter of the trimorphic monocotyledon Pontederia is grand. (682/3. This case interested Darwin as the only instance of heterostylism in Monocotyledons. See "Forms of Flowers," Edition II., page 183. F. Muller's paper is in the "Jenaische Zeitschrift," 1871.) I wonder whether I shall ever have time to recur to this subject; I hope I may, for I have a good deal of unpublished material.
Thank you for telling me about the first-formed flower having additional petals, stamens, carpels, etc., for it is a possible means of transition of form; it seems also connected with the fact on which I have insisted of peloric flowers being so often terminal. As pelorism is strongly inherited (and {I} have just got a curious case of this in a leguminous plant from India), would it not be worth while to fertilise some of your early flowers having additional organs with pollen from a similar flower, and see whether you could not make a race thus characterised? (682/4. See Letters 588, 589. Also "Variation under Domestication," Edition II., Volume I., pages 388-9.) Some of your Abutilons have germinated, but I have been very unfortunate with most of your seed.
You will remember having given me in a former letter an account of a very curious popular belief in regard to the subsequent progeny of asses, which have borne mules; and now I have another case almost exactly like that of Lord Morton's mare, in which it is said the shape of the hoofs in the subsequent progeny are affected. (Pangenesis will turn out true some day!) (682/5. See "Animals and Plants," Edition II., Volume I., page 435. For recent work on telegony see Ewart's "Experimental Investigations on Telegony," "Phil. Trans. R. Soc." 1899. A good account of the subject is given in the "Quarterly Review," 1899, page 404. See also Letter 275, Volume I.)
A few months ago I received an interesting letter and paper from your brother, who has taken up a new and good line of investigation, viz., the adaptation in insects for the fertilisation of flowers.
The only scientific man I have seen for several months is Kolliker, who came here with Gunther, and whom I liked extremely.
I am working away very hard at my book on man and on sexual selection, but I do not suppose I shall go to press till late in the autumn.
LETTER 683. TO F. MULLER. Down, January 1st, 1874.
No doubt I owe to your kindness two pamphlets received a few days ago, which have interested me in an extraordinary degree. (683/1. This refers to F. Muller's "Bestaubungsversuche an Abutilon-Arten" in the "Jenaische Zeitschr." Volume VII., which are thus referred to by Darwin ("Cross and Self Fert." pages 305-6): "Fritz Muller has shown by his valuable experiments on hybrid Abutilons, that the union of brothers and sisters, parents and children, and of other near relations is highly injurious to the fertility of the offspring." The Termite paper is in the same volume (viz., VII.) of the "Jenaische Zeitschr.") It is quite new to me what you show about the effects of relationship in hybrids—that is to say, as far as direct proof is concerned. I felt hardly any doubt on the subject, from the fact of hybrids becoming more fertile when grown in number in nursery gardens, exactly the reverse of what occurred with Gartner. (683/2. When many hybrids are grown together the pollination by near relatives is minimised.) The paper on Termites is even still more interesting, and the analogy with cleistogene flowers is wonderful. (683/3. On the back of his copy of Muller's paper Darwin wrote: "There exist imperfectly developed male and female Termites, with wings much shorter than those of queen and king, which serve to continue the species if a fully developed king and queen do not after swarming (which no doubt is for an occasional cross) enter {the} nest. Curiously like cleistogamic flowers.") The manner in which you refer to to my chapter on crossing is one of the most elegant compliments which I have ever received.
I have directed to be sent to you Belt's "Nicaragua," which seems to me the best Natural History book of travels ever published. Pray look to what he says about the leaf-carrying ant storing the leaves up in a minced state to generate mycelium, on which he supposes that the larvae feed. Now, could you open the stomachs of these ants and examine the contents, so as to prove or disprove this remarkable hypothesis? (683/4. The hypothesis has been completely confirmed by the researches of Moller, a nephew of F. Muller's: see his "Brasilische Pilzblumen" ("Botan. Mittheilgn. aus den Tropen," hrsg. von A.F.W. Schimper, Heft 7).)
LETTER 684. TO F. MULLER. Down, May 9th, 1877.
I have been particularly glad to receive your letter of March 25th on Pontederia, for I am now printing a small book on heterostyled plants, and on some allied subjects. I feel sure you will not object to my giving a short account of the flowers of the new species which you have sent me. I am the more anxious to do so as a writer in the United States has described a species, and seems to doubt whether it is heterostyled, for he thinks the difference in the length of the pistil depends merely on its growth! In my new book I shall use all the information and specimens which you have sent me with respect to the heterostyled plants, and your published notices.
One chapter will be devoted to cleistogamic species, and I will just notice your new grass case. My son Francis desires me to thank you much for your kindness with respect to the plants which bury their seeds.
I never fail to feel astonished, when I receive one of your letters, at the number of new facts you are continually observing. With respect to the great supposed subterranean animal, may not the belief have arisen from the natives having seen large skeletons embedded in cliffs? I remember finding on the banks of the Parana a skeleton of a Mastodon, and the Gauchos concluded that it was a borrowing animal like the Bizcacha. (684/1. On the supposed existence in Patagonia of a gigantic land-sloth, see "Natural Science," XIII., 1898, page 288, where Ameghino's discovery of the skin of Neomylodon listai was practically first made known, since his privately published pamphlet was not generally seen. The animal was afterwards identified with a Glossotherium, closely allied to Owen's G. Darwini, which has been named Glossotherium listai or Grypotherium domesticum. For a good account of the discoveries see Smith Woodward in "Natural Science," XV., 1899, page 351, where the literature is given.)
LETTER 685. TO F. MULLER. Down, May 14th {1877}.
I wrote to you a few days ago to thank you about Pontederia, and now I am going to ask you to add one more to the many kindnesses which you have done for me. I have made many observations on the waxy secretion on leaves which throw off water (e.g., cabbage, Tropoeolum), and I am now going to continue my observations. Does any sensitive species of Mimosa grow in your neighbourhood? If so, will you observe whether the leaflets keep shut during long-continued warm rain. I find that the leaflets open if they are continuously syringed with water at a temperature of about 19 deg C., but if the water is at a temperature of 33-35 deg C., they keep shut for more than two hours, and probably longer. If the plant is continuously shaken so as to imitate wind the leaflets soon open. How is this with the native plants during a windy day? I find that some other plants—for instance, Desmodium and Cassia—when syringed with water, place their leaves so that the drops fall quickly off; the position assumed differing somewhat from that in the so-called sleep. Would you be so kind as to observe whether any {other} plants place their leaves during rain so as to shoot off the water; and if there are any such I should be very glad of a leaf or two to ascertain whether they are coated with a waxy secretion. (685/1. See Letters 737-41.)
There is another and very different subject, about which I intend to write, and should be very glad of a little information. Are earthworms (Lumbricus) common in S. Brazil (685/2. F. Muller's reply is given in "Vegetable Mould," page 122.), and do they throw up on the surface of the ground numerous castings or vermicular masses such as we so commonly see in Europe? Are such castings found in the forests beneath the dead withered leaves? I am sure I can trust to your kindness to forgive me for asking you so many questions.
LETTER 686. TO F. MULLER. Down, July 24th, 1878.
Many thanks for the five kinds of seeds; all have germinated, and the Cassia seedlings have interested me much, and I daresay that I shall find something curious in the other plants. Nor have I alone profited, for Sir J. Hooker, who was here on Sunday, was very glad of some of the seeds for Kew. I am particularly obliged for the information about the earthworms. I suppose the soil in your forests is very loose, for in ground which has lately been dug in England the worms do not come to the surface, but deposit their castings in the midst of the loose soil.
I have some grand plants (and I formerly sent seeds to Kew) of the cleistogamic grass, but they show no signs of producing flowers of any kind as yet. Your case of the panicle with open flowers being sterile is parallel to that of Leersia oryzoides. I have always fancied that cross-fertilisation would perhaps make such panicles fertile. (686/1. The meaning of this sentence is somewhat obscure. Darwin apparently implies that the perfect flowers, borne on the panicles which occasionally emerge from the sheath, might be fertile if pollinated from another individual. See "Forms of Flowers," page 334.)
I am working away as hard as I can at all the multifarious kinds of movements of plants, and am trying to reduce them to some simple rules, but whether I shall succeed I do not know.
I have sent the curious lepidopteron case to Mr. Meldola.
LETTER 687. F. MULLER TO CHARLES DARWIN.
(687/1. In November, 1880, on receipt of an account of a flood in Brazil from which Fritz Muller had barely escaped with his life ("Life and Letters," III., 242); Darwin immediately wrote to Hermann Muller begging to be allowed to help in making good any loss in books or scientific instruments that his brother had sustained. It is this offer of help that is referred to in the first paragraph of the following letter: Darwin repeats the offer in Letter 690.)
Blumenau, Sa Catharina, Brazil, January 9th, 1881.
I do not know how to express {to} you my deep heartfelt gratitude for the generous offer which you made to my brother on hearing of the late dreadful flood of the Itajahy. From you, dear sir, I should have accepted assistance without hesitation if I had been in need of it; but fortunately, though we had to leave our house for more than a week, and on returning found it badly damaged, my losses have not been very great.
I must thank you also for your wonderful book on the movements of plants, which arrived here on New Year's Day. I think nobody else will have been delighted more than I was with the results which you have arrived at by so many admirably conducted experiments and observations; since I observed the spontaneous revolving movement of Alisma I had seen similar movements in so many and so different plants that I felt much inclined to consider spontaneous revolving movement or circumnutation as common to all plants and the movements of climbing plants as a special modification of that general phenomenon. And this you have now convincingly, nay, superabundantly, proved to be the case.
I was much struck with the fact that with you Maranta did not sleep for two nights after having its leaves violently shaken by wind, for here we have very cold nights only after storms from the west or south-west, and it would be very strange if the leaves of our numerous species of Marantaceae should be prevented by these storms to assume their usual nocturnal position, just when nocturnal radiation was most to be feared. It is rather strange, also, that Phaseolus vulgaris should not sleep during the early part of the summer, when the leaves are most likely to be injured during cold nights. On the contrary, it would not do any harm to many sub-tropical plants, that their leaves must be well illuminated during the day in order that they may assume at night a vertical position; for, in our climate at least, cold nights are always preceded by sunny days.
Of nearly allied plants sleeping very differently I can give you some more instances. In the genus Olyra (at least, in the one species observed by me) the leaves bend down vertically at night; now, in Endlicher's "Genera plantarum" this genus immediately precedes Strephium, the leaves of which you saw rising vertically.
In one of two species of Phyllanthus, growing as weeds near my house, the leaves of the erect branches bend upwards at night, while in the second species, with horizontal branches, they sleep like those of Phyllanthus Niruri or of Cassia. In this second species the tips of the branches also are curled downwards at night, by which movement the youngest leaves are yet better protected. From their vertical nyctitropic position the leaves of this Phyllanthus might return to horizontality, traversing 90 deg, in two ways, either to their own or to the opposite side of the branch; on the latter way no rotation would be required, while on the former each leaf must rotate on its own axis in order that its upper surface may be turned upwards. Thus the way to the wrong side appears to be even less troublesome. And indeed, in some rare cases I have seen three, four or even almost all the leaves of one side of a branch horizontally expanded on the opposite side, with their upper surfaces closely appressed to the lower surfaces of the leaves of that side.
This Phyllanthus agrees with Cassia not only in its manner of sleeping, but also by its leaves being paraheliotropic. (687/2. Paraheliotropism is the movement by which some leaves temporarily direct their edges to the source of light. See "Movements of Plants," page 445.) Like those of some Cassiae its leaves take an almost perfectly vertical position, when at noon, on a summer day, the sun is nearly in the zenith; but I doubt whether this paraheliotropism will be observable in England. To-day, though continuing to be fully exposed to the sun, at 3 p.m. the leaves had already returned to a nearly horizontal position. As soon as there are ripe seeds I will send you some; of our other species of Phyllanthus I enclose a few seeds in this letter.
In several species of Hedychium the lateral halves of the leaves when exposed to bright sunshine, bend downwards so that the lateral margins meet. It is curious that a hybrid Hedychium in my garden shows scarcely any trace of this paraheliotropism, while both the parent species are very paraheliotropic.
Might not the inequality of the cotyledons of Citrus and of Pachira be attributed to the pressure, which the several embryos enclosed in the same seed exert upon each other? I do not know Pachira aquatica, but {in} a species, of which I have a tree in my garden, all the seeds are polyembryonic, and so were almost all the seeds of Citrus which I examined. With Coffea arabica also seeds including two embryos are not very rare; but I have not yet observed whether in this case the cotyledons be inequal.
I repeated to-day Duval-Jouve's measurements on Bryophyllum calycinum (687/3. "Power of Movement in Plants," page 237. F. Muller's measurements show, however, that there is a tendency in the leaves to be more highly inclined at night than in the middle of the day, and so far they agree with Duval-Jouve's results.); but mine did not agree with his; they are as follows:—
Distances in mm. between the tips of the upper pair of leaves.
January 9th, 1881 3 A.M. 1 P.M. 6 P.M.
1st plant 54 43 36
2nd plant 28 25 23
3rd plant 28 27 27
4th plant 51 46 39
5th plant 61 52 45
_______________________________________________
222 193 170
LETTER 688. TO F. MULLER. Down, February 23rd, 1881.
Your letter has interested me greatly, as have so many during many past years. I thought that you would not object to my publishing in "Nature" (688/1. "Nature," March 3rd, 1881, page 409.) some of the more striking facts about the movements of plants, with a few remarks added to show the bearing of the facts. The case of the Phyllanthus (688/2. See Letter 687.), which turns up its leaves on the wrong side, is most extraordinary and ought to be further investigated. Do the leaflets sleep on the following night in the usual manner? Do the same leaflets on successive nights move in the same strange manner? I was particularly glad to hear of the strongly marked cases of paraheliotropism. I shall look out with much interest for the publication about the figs. (688/3. F. Muller published on Caprification in "Kosmos," 1882.) The creatures which you sketch are marvellous, and I should not have guessed that they were hymenoptera. Thirty or forty years ago I read all that I could find about caprification, and was utterly puzzled. I suggested to Dr. Cruger in Trinidad to investigate the wild figs, in relation to their cross-fertilisation, and just before he died he wrote that he had arrived at some very curious results, but he never published, as I believe, on the subject.
I am extremely glad that the inundation did not so greatly injure your scientific property, though it would have been a real pleasure to me to have been allowed to have replaced your scientific apparatus. (688/4. See Letter 687.) I do not believe that there is any one in the world who admires your zeal in science and wonderful powers of observation more than I do. I venture to say this, as I feel myself a very old man, who probably will not last much longer.
P.S.—With respect to Phyllanthus, I think that it would be a good experiment to cut off most of the leaflets on one side of the petiole, as soon as they are asleep and vertically dependent; when the pressure is thus removed, the opposite leaflets will perhaps bend beyond their vertically dependent position; if not, the main petiole might be a little twisted so that the upper surfaces of the dependent and now unprotected leaflets should face obliquely the sky when the morning comes. In this case diaheliotropism would perhaps conquer the ordinary movements of the leaves when they awake, and {assume} their diurnal horizontal position. As the leaflets are alternate, and as the upper surface will be somewhat exposed to the dawning light, it is perhaps diaheliotropism which explains your extraordinary case.
LETTER 689. TO F. MULLER. Down, April 12th, 1881.
I have delayed answering your last letter of February 25th, as I was just sending to the printers the MS. of a very little book on the habits of earthworms, of which I will of course send you a copy when published. I have been very much interested by your new facts on paraheliotropism, as I think that they justify my giving a name to this kind of movement, about which I long doubted. I have this morning drawn up an account of your observations, which I will send in a few days to "Nature." (689/1. "Nature," 1881, page 603. Curious facts are given on the movements of Cassia, Phyllanthus, sp., Desmodium sp. Cassia takes up a sunlight position unlike its own characteristic night-position, but resembling rather that of Haematoxylon (see "Power of Movement," figure 153, page 369). One species of Phyllanthus takes up in sunshine the nyctitropic attitude of another species. And the same sort of relation occurs in the genus Bauhinia.) I have thought that you would not object to my giving precedence to paraheliotropism, which has been so little noticed. I will send you a copy of "Nature" when published. I am glad that I was not in too great a hurry in publishing about Lagerstroemia. (689/2. Lagerstraemia was doubtfully placed among the heterostyled plants ("Forms of Flowers," page 167). F. Muller's observations showed that a totally different interpretation of the two sizes of stamen is possible. Namely, that one set serves merely to attract pollen-collecting bees, who in the act of visiting the flowers transfer the pollen of the longer stamens to other flowers. A case of this sort in Heeria, a Melastomad, was described by Muller ("Nature," August 4th, 1881, page 308), and the view was applied to the cases of Lagerstroemia and Heteranthera at a later date ("Nature," 1883, page 364). See Letters 620-30.) I have procured some plants of Melastomaceae, but I fear that they will not flower for two years, and I may be in my grave before I can repeat my trials. As far as I can imperfectly judge from my observations, the difference in colour of the anthers in this family depends on one set of anthers being partially aborted. I wrote to Kew to get plants with differently coloured anthers, but I learnt very little, as describers of dried plants do not attend to such points. I have, however, sowed seeds of two kinds, suggested to me as probable. I have, therefore, been extremely glad to receive the seeds of Heteranthera reniformis. As far as I can make out it is an aquatic plant; and whether I shall succeed in getting it to flower is doubtful. Will you be so kind as to send me a postcard telling me in what kind of station it grows. In the course of next autumn or winter, I think that I shall put together my notes (if they seem worth publishing) on the use or meaning of "bloom" (689/3. See Letters 736-40.), or the waxy secretion which makes some leaves glaucous. I think that I told you that my experiments had led me to suspect that the movement of the leaves of Mimosa, Desmodium and Cassia, when shaken and syringed, was to shoot off the drops of water. If you are caught in heavy rain, I should be very much obliged if you would keep this notion in your mind, and look to the position of such leaves. You have such wonderful powers of observation that your opinion would be more valued by me than that of any other man. I have among my notes one letter from you on the subject, but I forget its purport. I hope, also, that you may be led to follow up your very ingenious and novel view on the two-coloured anthers or pollen, and observe which kind is most gathered by bees.
LETTER 690. TO F. MULLER. {Patterdale}, June 21st, 1881.
I should be much obliged if you could without much trouble send me seeds of any heterostyled herbaceous plants (i.e. a species which would flower soon), as it would be easy work for me to raise some illegitimate seedlings to test their degree of infertility. The plant ought not to have very small flowers. I hope that you received the copies of "Nature," with extracts from your interesting letters (690/1. "Nature," March 3rd, 1881, Volume XXIII., page 409, contains a letter from C. Darwin on "Movements of Plants," with extracts from Fritz Muller's letter. Another letter, "On the Movements of Leaves," was published in "Nature," April 28th, 1881, page 603, with notes on leaf-movements sent to Darwin by Muller.), and I was glad to see a notice in "Kosmos" on Phyllanthus. (690/2. "Verirrte Blatter," by Fritz Muller ("Kosmos," Volume V., page 141, 1881). In this article an account is given of a species of Phyllanthus, a weed in Muller's garden. See Letter 687.) I am writing this note away from my home, but before I left I had the satisfaction of seeing Phyllanthus sleeping. Some of the seeds which you so kindly sent me would not germinate, or had not then germinated. I received a letter yesterday from Dr. Breitenbach, and he tells me that you lost many of your books in the desolating flood from which you suffered. Forgive me, but why should you not order, through your brother Hermann, books, etc., to the amount of 100 pounds, and I would send a cheque to him as soon as I heard the exact amount? This would be no inconvenience to me; on the contrary, it would be an honour and lasting pleasure to me to have aided you in your invaluable scientific work to this small and trifling extent. (690/3. See Letter 687, also "Life and Letters," III., page 242.)
LETTER 691. TO F. MULLER.
(691/1. The following extract from a letter to F. Muller shows what was the nature of Darwin's interest in the effect of carbonate of ammonia on roots, etc. He was, we think, wrong in adhering to the belief that the movements of aggregated masses are of an amoeboid nature. The masses change shape, just as clouds do under the moulding action of the wind. In the plant cell the moulding agent is the flowing protoplasm, but the masses themselves are passive.)
September 10th, 1881.
Perhaps you may remember that I described in "Insectivorous Plants" a really curious phenomenon, which I called the aggregation of the protoplasm in the cells of the tentacles. None of the great German botanists will admit that the moving masses are composed of protoplasm, though it is astonishing to me that any one could watch the movement and doubt its nature. But these doubts have led me to observe analogous facts, and I hope to succeed in proving my case.
LETTER 692. TO F. MULLER. Down, November 13th, 1881.
I received a few days ago a small box (registered) containing dried flower-heads with brown seeds somewhat sculptured on the sides. There was no name, and I should be much obliged if some time you would tell me what these seeds are. I have planted them.
I sent you some time ago my little book on earthworms, which, though of no importance, has been largely read in England. I have little or nothing to tell you about myself. I have for a couple of months been observing the effects of carbonate of ammonia on chlorophyll and on the roots of certain plants (692/1. Published under the title "The Action of Carbonate of Ammonia on the Roots of Certain Plants and on Chlorophyll Bodies," "Linn. Soc. Journ." XIX., 1882, pages 239-61, 262-84.), but the subject is too difficult for me, and I cannot understand the meaning of some strange facts which I have observed. The mere recording new facts is but dull work.
Professor Wiesner has published a book (692/2. See Letter 763.), giving a different explanation to almost every fact which I have given in my "Power of Movement in Plants." I am glad to say that he admits that almost all my statements are true. I am convinced that many of his interpretations of the facts are wrong, and I am glad to hear that Professor Pfeffer is of the same opinion; but I believe that he is right and I wrong on some points. I have not the courage to retry all my experiments, but I hope to get my son Francis to try some fresh ones to test Wiesner's explanations. But I do not know why I have troubled you with all this.
LETTER 693. TO F. MULLER. {4, Bryanston Street}, December 19th, 1881.
I hope that you may find time to go on with your experiments on such plants as Lagerstroemia, mentioned in your letter of October 29th, for I believe you will arrive at new and curious results, more especially if you can raise two sets of seedlings from the two kinds of pollen.
Many thanks for the facts about the effect of rain and mud in relation to the waxy secretion. I have observed many instances of the lower side being protected better than the upper side, in the case, as I believe, of bushes and trees, so that the advantage in low-growing plants is probably only an incidental one. (693/1. The meaning is here obscure: it appears to us that the significance of bloom on the lower surface of the leaves of both trees and herbs depends on the frequency with which all or a majority of the stomata are on the lower surface—where they are better protected from wet (even without the help of bloom) than on the exposed upper surface. On the correlation between bloom and stomata, see Francis Darwin "Linn. Soc. Journ." XXII., page 99.) As I am writing away from my home, I have been unwilling to try more than one leaf of the Passiflora, and this came out of the water quite dry on the lower surface and quite wet on the upper. I have not yet begun to put my notes together on this subject, and do not at all know whether I shall be able to make much of it. The oddest little fact which I have observed is that with Trifolium resupinatum, one half of the leaf (I think the right-hand side, when the leaf is viewed from the apex) is protected by waxy secretion, and not the other half (693/2. In the above passage "leaf" should be "leaflet": for a figure of Trifolium resupinatum see Letter 740.); so that when the leaf is dipped into water, exactly half the leaf comes out dry and half wet. What the meaning of this can be I cannot even conjecture. I read last night your very interesting article in "Kosmos" on Crotalaria, and so was very glad to see the dried leaves sent by you: it seems to me a very curious case. I rather doubt whether it will apply to Lupinus, for, unless my memory deceives me, all the leaves of the same plant sometimes behaved in the same manner; but I will try and get some of the same seeds of the Lupinus, and sow them in the spring. Old age, however, is telling on me, and it troubles me to have more than one subject at a time on hand.
(693/3. In a letter to F. Muller (September 10, 1881) occurs a sentence which may appropriately close this series: "I often feel rather ashamed of myself for asking for so many things from you, and for taking up so much of your valuable time, but I can assure you that I feel grateful.")
2.XI.III. MISCELLANEOUS, 1868-1881.
LETTER 694. TO G. BENTHAM. Down, April 22nd, 1868.
I have been extremely much pleased by your letter, and I take it as a very great compliment that you should have written to me at such length...I am not at all surprised that you cannot digest pangenesis: it is enough to give any one an indigestion; but to my mind the idea has been an immense relief, as I could not endure to keep so many large classes of facts all floating loose in my mind without some thread of connection to tie them together in a tangible method.
With respect to the men who have recently written on the crossing of plants, I can at present remember only Hildebrand, Fritz Muller, Delpino, and G. Henslow; but I think there are others. I feel sure that Hildebrand is a very good observer, for I have read all his papers, and during the last twenty years I have made unpublished observations on many of the plants which he describes. {Most of the criticisms which I sometimes meet with in French works against the frequency of crossing I am certain are the result of mere ignorance. I have never hitherto found the rule to fail that when an author describes the structure of a flower as specially adapted for self-fertilisation, it is really adapted for crossing. The Fumariaceae offer a good instance of this, and Treviranus threw this order in my teeth; but in Corydalis Hildebrand shows how utterly false the idea of self-fertilisation is. This author's paper on Salvia (694/1. Hildebrand, "Pringsheim's Jahrbucher," IV.) is really worth reading, and I have observed some species, and know that he is accurate}. (694/2. The passage within {} was published in the "Life and Letters," III., page 279.) Judging from a long review in the "Bot. Zeitung", and from what I know of some the plants, I believe Delpino's article especially on the Apocynaea, is excellent; but I cannot read Italian. (694/3. Hildebrand's paper in the "Bot. Zeitung," 1867, refers to Delpino's work on the Asclepiads, Apocyneae and other Orders.) Perhaps you would like just to glance at such pamphlets as I can lay my hands on, and therefore I will send them, as if you do not care to see them you can return them at once; and this will cause you less trouble than writing to say you do not care to see them. With respect to Primula, and one point about which I feel positive is that the Bardfield and common oxlips are fundamentally distinct plants, and that the common oxlip is a sterile hybrid. (694/4. For a general account of the Bardfield oxlip (Primula elatior) see Miller Christy, "Linn. Soc. Journ." Volume XXXIII., page 172, 1897.) I have never heard of the common oxlip being found in great abundance anywhere, and some amount of difference in number might depend on so small a circumstance as the presence of some moth which habitually sucked the primrose and cowslip. To return to the subject of crossing: I am experimenting on a very large scale on the difference in power and growth between plants raised from self-fertilised and crossed seeds, and it is no exaggeration to say that the difference in growth and vigour is sometimes truly wonderful. Lyell, Huxley, and Hooker have seen some of my plants, and been astonished; and I should much like to show them to you. I always supposed until lately that no evil effects would be visible until after several generations of self-fertilisation, but now I see that one generation sometimes suffices, and the existence of dimorphic plants and all the wonderful contrivances of orchids are quite intelligible to me.
LETTER 695. TO T.H. FARRER (Lord Farrer). Down, June 5th, 1868.
I must write a line to cry peccavi. I have seen the action in Ophrys exactly as you describe, and am thoroughly ashamed of my inaccuracy. (695/1. See "Fertilisation of Orchids," Edition II., page 46, where Lord Farrer's observations on the movement of the pollinia in Ophrys muscifera are given.) I find that the pollinia do not move if kept in a very damp atmosphere under a glass; so that it is just possible, though very improbable, that I may have observed them during a very damp day.
I am not much surprised that I overlooked the movement in Habenaria, as it takes so long. (695/2. This refers to Peristylus viridis, sometimes known as Habenaria viridis. Lord Farrer's observations are given in "Fertilisation of Orchids," Edition II., page 63.)
I am glad you have seen Listera; it requires to be seen to believe in the co-ordination in the position of the parts, the irritability, and the chemical nature of the viscid fluid. This reminds me that I carefully described to Huxley the shooting out of the pollinia in Catasetum, and received for an answer, "Do you really think that I can believe all that!" (695/3. See Letter 665.)
LETTER 696. TO J.D. HOOKER. Down, December 2nd, 1868.
It is a splendid scheme, and if you make only a beginning on a "Flora," which shall serve as an index to all papers on curious points in the life-history of plants, you will do an inestimable good service. Quite recently I was asked by a man how he could find out what was known on various biological points in our plants, and I answered that I knew of no such book, and that he might ask half a dozen botanists before one would chance to remember what had been published on this or that point. Not long ago another man, who had been experimenting on the quasi-bulbs on the leaves of Cardamine, wrote to me to complain that he could not find out what was known on the subject. It is almost certain that some early or even advanced students, if they found in their "Flora" a line or two on various curious points, with references for further investigation, would be led to make further observations. For instance, a reference to the viscid threads emitted by the seeds of Compositae, to the apparatus (if it has been described) by which Oxalis spurts out its seeds, to the sensitiveness of the young leaves of Oxalis acetosella with reference to O. sensitiva. Under Lathyrus nissolia it would {be} better to refer to my hypothetical explanation of the grass-like leaves than to nothing. (696/1. No doubt the view given in "Climbing Plants," page 201, that L. nissolia has been evolved from a form like L. aphaca.) Under a twining plant you might say that the upper part of the shoot steadily revolves with or against the sun, and so, when it strikes against any object it turns to the right or left, as the case may be. If, again, references were given to the parasitism of Euphrasia, etc., how likely it would be that some young man would go on with the investigation; and so with endless other facts. I am quite enthusiastic about your idea; it is a grand idea to make a "Flora" a guide for knowledge already acquired and to be acquired. I have amused myself by speculating what an enormous number of subjects ought to be introduced into a Eutopian (696/2. A mis-spelling of Utopian.) Flora, on the quickness of the germination of the seeds, on their means of dispersal; on the fertilisation of the flower, and on a score of other points, about almost all of which we are profoundly ignorant. I am glad to read what you say about Bentham, for my inner consciousness tells me that he has run too many forms together. Should you care to see an elaborate German pamphlet by Hermann Muller on the gradation and distinction of the forms of Epipactis and of Platanthera? (696/3. "Verhand. d. Nat. Ver. f. Pr. Rh. u. Wesfal." Jahrg. XXV.: see "Fertilisation of Orchids," Edition II., pages 74, 102.) It may be absurd in me to suggest, but I think you would find curious facts and references in Lecoq's enormous book (696/4. "Geographie Botanique," 9 volumes, 1854-58.), in Vaucher's four volumes (696/5. "Plantes d'Europe," 4 volumes, 1841.), in Hildebrand's "Geschlechter Vertheilung" (696/6 "Geschlechter Vertheilung bei den Pflanzen," 1 volume, Leipzig, 1867.), and perhaps in Fournier's "De la Fecondation." (696/7. "De la Fecondation dans les Phanerogames," par Eugene Fournier: thesis published in Paris in 1863. The facts noted in Darwin's copy are the explosive stamens of Parietaria, the submerged flowers of Alisma containing air, the manner of fertilisation of Lopezia, etc.) I wish you all success in your gigantic undertaking; but what a pity you did not think of it ten years ago, so as to have accumulated references on all sorts of subjects. Depend upon it, you will have started a new era in the floras of various countries. I can well believe that Mrs. Hooker will be of the greatest possible use to you in lightening your labours and arranging your materials.
LETTER 697. TO J.D. HOOKER. Down, December 5th, 1868.
...Now I want to beg for assistance for the new edition of "Origin." Nageli himself urges that plants offer many morphological differences, which from being of no service cannot have been selected, and which he accounts for by an innate principle of progressive development. (697/1. Nageli's "Enstehung und Begriff der Naturhistorischen Art." An address delivered at the public session of the Royal Academy of Sciences of Munich, March 28th, 1865; published by the Academy. Darwin's copy is the 2nd edition; it bears signs, in the pencilled notes on the margins, of having been read with interest. Much of it was translated for him by a German lady, whose version lies with the original among his pamphlets. At page 27 Nageli writes: "It is remarkable that the useful adaptations which Darwin brings forward in the case of animals, and which may be discovered in numbers among plants, are exclusively of a physiological kind, that they always show the formation or transformation of an organ to a special function. I do not know among plants a morphological modification which can be explained on utilitarian principles." Opposite this passage Darwin has written "a very good objection": but Nageli's sentence seems to us to be of the nature of a truism, for it is clear that any structure whose evolution can be believed to have come about by Natural Selection must have a function, and the case falls into the physiological category. The various meanings given to the term morphological makes another difficulty. Nageli cannot use it in the sense of "structural"—in which sense it is often applied, since that would mean that no plant structures have a utilitarian origin. The essence of morphology (in the better and more precise sense) is descent; thus we say that a pollen-grain is morphologically a microspore. And this very example serves to show the falseness of Nageli's view, since a pollen-grain is an adaptation to aerial as opposed to aquatic fertilisation. In the 5th edition of the "Origin," 1869, page 151, Darwin discusses Nageli's essay, confining himself to the simpler statement that there are many structural characters in plants to which we cannot assign uses. See Volume I., Letter 207.) I find old notes about this difficulty; but I have hitherto slurred it over. Nageli gives as instances the alternate and spiral arrangement of leaves, and the arrangement of the cells in the tissues. Would you not consider as a morphological difference the trimerous, tetramerous, etc., divisions of flowers, the ovules being erect or suspended, their attachment being parietal or placental, and even the shape of the seed when of no service to the plant.
Now, I have thought, and want to show, that such differences follow in some unexplained manner from the growth or development of plants which have passed through a long series of adaptive changes. Anyhow, I want to show that these differences do not support the idea of progressive development. Cassini states that the ovaria on the circumference and centre of Compos. flowers differ in essential characters, and so do the seeds in sculpture. The seeds of Umbelliferae in the same relative positions are coelospermous and orthospermous. There is a case given by Augt. St. Hilaire of an erect and suspended ovule in the same ovarium, but perhaps this hardly bears on the point. The summit flower, in Adoxa and rue differ from the lower flowers. What is the difference in flowers of the rue? how is the ovarium, especially in the rue? As Augt. St. Hilaire insists on the locularity of the ovarium varying on the same plant in some of the Rutaceae, such differences do not speak, as it seems to me, in favour of progressive development. Will you turn the subject in your mind, and tell me any more facts. Difference in structure in flowers in different parts of the same plant seems best to show that they are the result of growth or position or amount of nutriment.
I have got your photograph (697/2. A photograph by Mrs. Cameron.) over my chimneypiece, and like it much; but you look down so sharp on me that I shall never be bold enough to wriggle myself out of any contradiction.
Owen pitches into me and Lyell in grand style in the last chapter of volume 3 of "Anat. of Vertebrates." He is a cool hand. He puts words from me in inverted commas and alters them. (697/3. The passage referred to seems to be in Owen's "Anatomy of Vertebrata," III., pages 798, 799, note. "I deeply regretted, therefore, to see in a 'Historical Sketch' of the Progress of Enquiry into the origin of species, prefixed to the fourth edition of that work (1866), that Mr. Darwin, after affirming inaccurately and without evidence, that I admitted Natural Selection to have done something toward that end, to wit, the 'origin of species,' proceeds to remark: 'It is surprising that this admission should not have been made earlier, as Prof. Owen now believes that he promulgated the theory of Natural Selection in a passage read before the Zoological Society in February, 1850, ("Trans." Volume IV., page 15).'" The first of the two passages quoted by Owen from the fourth edition of the "Origin" runs: "Yet he {Prof. Owen} at the same time admits that Natural Selection MAY {our italics} have done something towards this end." In the sixth edition of the "Origin," page xviii., Darwin, after referring to a correspondence in the "London Review" between the Editor of that Journal and Owen, goes on: "It appeared manifest to the editor, as well as to myself, that Prof. Owen claimed to have promulgated the theory of Natural Selection before I had done so;...but as far as it is possible to understand certain recently published passages (Ibid. {"Anat. of Vert."}, Volume III., page 798), I have either partly or wholly again fallen into error. It is consolatory to me that others find Prof. Owen's controversial writings as difficult to understand and to reconcile with each other, as I do. As far as the mere enunciation of the principle of Natural Selection is concerned, it is quite immaterial whether or no Prof. Owen preceded me, for both of us, as shown in this historical sketch, were long ago preceded by Dr. Wells and Mr. Matthews.")
LETTER 698. TO J.D. HOOKER. Down, December 29th, 1868.
Your letter is quite invaluable, for Nageli's essay (698/1. See preceding Letter.) is so clever that it will, and indeed I know it has produced a great effect; so that I shall devote three or four pages to an answer. I have been particularly struck by your statements about erect and suspended ovules. You have given me heart, and I will fight my battle better than I should otherwise have done. I think I cannot resist throwing the contrivances in orchids into his teeth. You say nothing about the flowers of the rue. (698/2. For Ruta see "Origin," Edition V., page 154.) Ask your colleagues whether they know anything about the structure of the flower and ovarium in the uppermost flower. But don't answer on purpose.
I have gone through my long Index of "Gardeners' Chronicle," which was made solely for my own use, and am greatly disappointed to find, as I fear, hardly anything which will be of use to you. (698/3. For Hooker's projected biological book, see Letter 696.) I send such as I have for the chance of their being of use.
LETTER 699. TO J.D. HOOKER. Down, January 16th {1869}.
Your two notes and remarks are of the utmost value, and I am greatly obliged to you for your criticism on the term. "Morphological" seems quite just, but I do not see how I can avoid using it. I found, after writing to you, in Vaucher about the Rue (699/1. "Plantes d'Europe," Volume I., page 559, 1841.), but from what you say I will speak more cautiously. It is the Spanish Chesnut that varies in divergence. Seeds named Viola nana were sent me from Calcutta by Scott. I must refer to the plants as an "Indian species," for though they have produced hundreds of closed flowers, they have not borne one perfect flower. (699/2. The cleistogamic flowers of Viola are used in the discussion on Nageli's views. See "Origin," Edition V., page 153.) You ask whether I want illustrations "of ovules differing in position in different flowers on the same plant." If you know of such cases, I should certainly much like to hear them. Again you speak of the angle of leaf-divergence varying and the variations being transmitted. Was the latter point put in in a hurry to round the sentence, or do you really know of cases?
Whilst looking for notes on the variability of the divisions of the ovarium, position of the ovules, aestivation, etc., I found remarks written fifteen or twenty years ago, showing that I then supposed that characters which were nearly uniform throughout whole groups must be of high vital importance to the plants themselves; consequently I was greatly puzzled how, with organisms having very different habits of life, this uniformity could have been acquired through Natural Selection. Now, I am much inclined to believe, in accordance with the view given towards the close of my MS., that the near approach to uniformity in such structures depends on their not being of vital importance, and therefore not being acted on by Natural Selection. (699/3. This view is given in the "Origin," Edition VI., page 372.) If you have reflected on this point, what do you think of it? I hope that you approved of the argument deduced from the modifications in the small closed flowers.
It is only about two years since last edition of "Origin," and I am fairly disgusted to find how much I have to modify, and how much I ought to add; but I have determined not to add much. Fleeming Jenkin has given me much trouble, but has been of more real use to me than any other essay or review. (699/4. On Fleeming Jenkin's review, "N. British Review," June, 1867, see "Life and Letters," III., page 107.)
LETTER 700. TO J.D. HOOKER. Down {January 22nd, 1869}.
Your letter is quite splenditious. I am greatly tempted, but shall, I hope, refrain from using some of your remarks in my chapter on Classification. It is very true what you say about unimportant characters being so important systematically; yet it is hardly paradoxical bearing in mind that the natural system is genetic, and that we have to discover the genealogies anyhow. Hence such parts as organs of generation are so useful for classification though not concerned with the manner of life. Hence use for same purpose of rudimentary organs, etc. You cannot think what a relief it is that you do not object to this view, for it removes PARTLY a heavy burden from my shoulders. If I lived twenty more years and was able to work, how I should have to modify the "Origin," and how much the views on all points will have to be modified! Well, it is a beginning, and that is something...
LETTER 701. TO T.H. FARRER (Lord Farrer). Down, August 10th, 1869.
Your view seems most ingenious and probable; but ascertain in a good many cases that the nectar is actually within the staminal tube. (701/1. It seems that Darwin did not know that the staminal tube in the diadelphous Leguminosae serves as a nectar-holder, and this is surprising, as Sprengel was aware of the fact.) One can see that if there is to be a split in the tube, the law of symmetry would lead it to be double, and so free one stamen. Your view, if confirmed, would be extremely well worth publication before the Linnean Society. It is to me delightful to see what appears a mere morphological character found to be of use. It pleases me the more as Carl Nageli has lately been pitching into me on this head. Hooker, with whom I discussed the subject, maintained that uses would be found for lots more structures, and cheered me by throwing my own orchids into my teeth. (701/2. See Letters 697-700.)
All that you say about changed position of the peduncle in bud, in flower, and in seed, is quite new to me, and reminds me of analogous cases with tendrils. (701/3. See Vochting, "Bewegung der Bluthen und Fruchte," 1882; also Kerner, "Pflanzenleben," Volume I., page 494, Volume II., page 121.) This is well worth working out, and I dare say the brush of the stigma.
With respect to the hairs or filaments (about which I once spoke) within different parts of flowers, I have a splendid Tacsonia with perfectly pendent flowers, and there is only a microscopical vestige of the corona of coloured filaments; whilst in most common passion-flowers the flowers stand upright, and there is the splendid corona which apparently would catch pollen. (701/4. Sprengel ("Entdeckte Geheimniss," page 164) imagined that the crown of the Passion-flower served as a nectar-guide and as a platform for insects, while other rings of filaments served to keep rain from the nectar. F. Muller, quoted in H. Muller ("Fertilisation," page 268), looks at the crowns of hairs, ridges in some species, etc., as gratings serving to imprison flies which attract the fertilising humming-birds. There is, we believe, no evidence that the corona catches pollen. See Letter 704, note.)
On the lower side of corolla of foxglove there are some fine hairs, but these seem of not the least use (701/5. It has been suggested that the hairs serve as a ladder for humble bees; also that they serve to keep out "unbidden guests.")—a mere purposeless exaggeration of down on outside—as I conclude after watching the bees at work, and afterwards covering up some plants; for the protected flowers rarely set any seed, so that the hairy lower part of corolla does not come into contact with stigma, as some Frenchman says occurs with some other plants, as Viola odorata and I think Iris.
I heartily wish I could accept your kind invitation, for I am not by nature a savage, but it is impossible. Forgive my dreadful handwriting, none of my womenkind are about to act as amanuensis.
LETTER 702. TO WILLIAM C. TAIT.
(702/1. Mr. Tait, to whom the following letter is addressed, was resident in Portugal. His kindness in sending plants of Drosophyllum lusitanicum is acknowledged in "Insectivorous Plants.")
Down, March 12th, 1869.
I have received your two letters of March 2nd and 5th, and I really do not know how to thank you enough for your extraordinary kindness and energy. I am glad to hear that the inhabitants notice the power of the Drosophyllum to catch flies, for this is the subject of my studies. (702/2. The natives are said to hang up plants of Drosophyllum in their cottages to act as fly-papers ("Insectivorous Plants," page 332).) I have observed during several years the manner in which this is effected, and the results produced in several species of Drosera, and in the wonderful American Dionoea, the leaves of which catch insects just like a steel rat-trap. Hence I was most anxious to learn how the Drosophyllum would act, so that the Director of the Royal Gardens at Kew wrote some years ago to Portugal to obtain specimens for me, but quite failed. So you see what a favour you have conferred on me. With Drosera it is nothing less than marvellous how minute a fraction of a grain of any nitrogenised matter the plant can detect; and how differently it behaves when matter, not containing nitrogen, of the same consistence, whether fluid or solid, is applied to the glands. It is also exquisitely sensitive to a weight of even the 1/70000 of a grain. From what I can see of the glands on Drosophyllum I suspect that I shall find only the commencement, or nascent state of the wonderful capacities of the Drosera, and this will be eminently interesting to me. My MS. on this subject has been nearly ready for publication during some years, but when I shall have strength and time to publish I know not.
And now to turn to other points in your letter. I am quite ignorant of ferns, and cannot name your specimen. The variability of ferns passes all bounds. With respect to your Laugher Pigeons, if the same with the two sub-breeds which I kept, I feel sure from the structure of the skeleton, etc., that it is a descendant of C. livia. In regard to beauty, I do not feel the difficulty which you and some others experience. In the last edition of my "Origin" I have discussed the question, but necessarily very briefly. (702/3. Fourth Edition, page 238.) A new and I hope amended edition of the "Origin" is now passing through the press, and will be published in a month or two, and it will give me great pleasure to send you a copy. Is there any place in London where parcels are received for you, or shall I send it by post? With reference to dogs' tails, no doubt you are aware that a rudimentary stump is regularly inherited by certain breeds of sheep-dogs, and by Manx cats. You speak of a change in the position of the axis of the earth: this is a subject quite beyond me, but I believe the astronomers reject the idea. Nevertheless, I have long suspected that some periodical astronomical or cosmical cause must be the agent of the incessant oscillations of level in the earth's crust. About a month ago I suggested this to a man well capable of judging, but he could not conceive any such agency; he promised, however, to keep it in mind. I wish I had time and strength to write to you more fully. I had intended to send this letter off at once, but on reflection will keep it till I receive the plants.
LETTER 703. TO H. MULLER. Down, March 14th, 1870.
I think you have set yourself a new, very interesting, and difficult line of research. As far as I know, no one has carefully observed the structure of insects in relation to flowers, although so many have now attended to the converse relation. (703/1. See Letter 462, also H. Muller, "Fertilisation of Flowers," English Translation, page 30, on "The insects which visit flowers." In Muller's book references are given to several of his papers on this subject.) As I imagine few or no insects are adapted to suck the nectar or gather the pollen of any single family of plants, such striking adaptations can hardly, I presume, be expected in insects as in flowers.
LETTER 704. TO T.H. FARRER (Lord Farrer).
Down, May 28th, 1870.
I suppose I must have known that the stamens recovered their former position in Berberis (704/1. See Farrer, "Nature," II., 1870, page 164. Lord Farrer was before H. Muller in making out the mechanism of the barberry.), for I formerly tried experiments with anaesthetics, but I had forgotten the facts, and I quite agree with you that it is a sound argument that the movement is not for self-fertilisation. The N. American barberries (Mahonia) offer a good proof to what an extent natural crossing goes on in this genus; for it is now almost impossible in this country to procure a true specimen of the two or three forms originally introduced.
I hope the seeds of Passiflora will germinate, for the turning up of the pendent flower must be full of meaning. (704/2. Darwin had (May 12th, 1870) sent to Farrer an extract from a letter from F. Muller, containing a description of a Passiflora visited by humming-birds, in which the long flower-stalk curls up so that "the flower itself is upright." Another species visited by bees is described as having "dependent flowers." In a letter, June 29th, 1870, Mr. Farrer had suggested that P. princeps, which he described as having sub-erect flowers, is fitted for humming-birds' visits. In another letter, October 13th, 1869, he says that Tacsonia, which has pendent flowers and no corona, is not fertilised by insects in English glass-houses, and may be adapted for humming-birds. See "Life and Letters," III., page 279, for Farrer's remarks on Tacsonia and Passiflora; also H. Muller's "Fertilisation of Flowers," page 268, for what little is known on the subject; also Letter 701 in the present volume.) I am so glad that you are able to occupy yourself a little with flowers: I am sure it is most wise in you, for your own sake and children's sakes.
Some little time ago Delpino wrote to me praising the Swedish book on the fertilisation of plants; as my son George can read a little Swedish, I should like to have it back for a time, just to hear a little what it is about, if you would be so kind as to return it by book-post. (704/3. Severin Axell, "Om anordningarna for de Fanerogama Vaxternas Befruktning," Stockholm, 1869.)
I am going steadily on with my experiments on the comparative growth of crossed and self-fertilised plants, and am now coming to some very curious anomalies and some interesting results. I forget whether I showed you any of them when you were here for a few hours. You ought to see them, as they explain at a glance why Nature has taken such extraordinary pains to ensure frequent crosses between distinct individuals.
If in the course of the summer you should feel any inclination to come here for a day or two, I hope that you will propose to do so, for we should be delighted to see you...
LETTER 705. TO ASA GRAY. Down, December 7th, 1870.
I have been very glad to receive your letter this morning. I have for some time been wishing to write to you, but have been half worked to death in correcting my uncouth English for my new book. (705/1. "Descent of Man.") I have been glad to hear of your cases appearing like incipient dimorphism. I believe that they are due to mere variability, and have no significance. I found a good instance in Nolana prostrata, and experimented on it, but the forms did not differ in fertility. So it was with Amsinckia, of which you told me. I have long thought that such variations afforded the basis for the development of dimorphism. I was not aware of such cases in Phlox, but have often admired the arrangement of the anthers, causing them to be all raked by an inserted proboscis. I am glad also to hear of your curious case of variability in ovules, etc.
I said that I had been wishing to write to you, and this was about your Drosera, which after many fluctuations between life and death, at last made a shoot which I could observe. The case is rather interesting; but I must first remind you that the filament of Dionoea is not sensitive to very light prolonged pressure, or to nitrogenous matter, but is exquisitely sensitive to the slightest touch. (705/2. In another connection the following reference to Dionoea is of some interest: "I am sure I never heard of Curtis's observations on Dionoea, nor have I met with anything more than general statements about this plant or about Nepenthes catching insects." (From a letter to Sir J.D. Hooker, July 12th, 1860.)) In our Drosera the filaments are not sensitive to a slight touch, but are sensitive to prolonged pressure from the smallest object of any nature; they are also sensitive to solid or fluid nitrogenous matter. Now in your Drosera the filaments are not sensitive to a rough touch or to any pressure from non-nitrogenous matter, but are sensitive to solid or fluid nitrogenous matter. (705/3. Drosera filiformis: see "Insectivorous Plants," page 281. The above account does not entirely agree with Darwin's published statement. The filaments moved when bits of cork or cinder were placed on them; they did not, however, respond to repeated touches with a needle, thus behaving differently from D. rotundifolia. It should be remembered that the last-named species is somewhat variable in reacting to repeated touches.) Is it not curious that there should be such diversified sensitiveness in allied plants?
I received a very obliging letter from Mr. Morgan, but did not see him, as I think he said he was going to start at once for the Continent. I am sorry to hear rather a poor account of Mrs. Gray, to whom my wife and I both beg to be very kindly remembered.
LETTER 706. TO C.V. RILEY.
(706/1. In Riley's opinion his most important work was the series entitled "Annual Report on the Noxious, Beneficial, and other Insects of the State of Missouri" (Jefferson City), beginning in 1869. These reports were greatly admired by Mr. Darwin, and his copies of them, especially of Nos. 3 and 4, show signs of careful reading.)
Down, June 1st {1871}.
I received some little time ago your report on noxious insects, and have now read the whole with the greatest interest. (706/2. "Third Annual Report on the Noxious, Beneficial, and other Insects of the State of Missouri" (Jefferson City, Mo.). The mimetic case occurs at page 67; the 1875 pupae of Pterophorus periscelidactylus, the "Grapevine Plume," have pupae either green or reddish brown, the former variety being found on the leaves, the latter on the brown stems of the vine.) There are a vast number of facts and generalisations of value to me, and I am struck with admiration at your powers of observation.
The discussion on mimetic insects seems to me particularly good and original. Pray accept my cordial thanks for the instruction and interest which I have received.
What a loss to Natural Science our poor mutual friend Walsh has been; it is a loss ever to be deplored...
Your country is far ahead of ours in some respects; our Parliament would think any man mad who should propose to appoint a State Entomologist.
LETTER 707A. TO C.V. RILEY.
(706A/1. We have found it convenient to place the two letters to Riley together, rather than separate them chronologically.)
Down, September 28th, 1881.
I must write half a dozen lines to say how much interested I have been by your "Further Notes" on Pronuba which you were so kind as to send me. (706A/2. "Proc. Amer. Assoc. Adv. Sci." 1880.) I had read the various criticisms, and though I did not know what answer could be made, yet I felt full confidence in your result, and now I see that I was right...If you make any further observation on Pronuba it would, I think, be well worth while for you to observe whether the moth can or does occasionally bring pollen from one plant to the stigma of a distinct one (706A/3. Riley discovered the remarkable fact that the Yucca moth (Pronuba yuccasella) lays its eggs in the ovary of Yucca flowers, which it has previously pollinated, thus making sure of a supply of ovules for the larvae.), for I have shown that the cross-fertilisation of the flowers on the same plant does very little good; and, if I am not mistaken, you believe that Pronuba gathers pollen from the same flower which she fertilises.
What interesting and beautiful observations you have made on the metamorphoses of the grasshopper-destroying insects.
LETTER 707. TO F. HILDEBRAND. Down, February 9th {1872}.
Owing to other occupations I was able to read only yesterday your paper on the dispersal of the seeds of Compositae. (707/1. "Ueber die Verbreitungsmittel der Compositenfruchte." "Bot. Zeitung," 1872, page 1.) Some of the facts which you mention are extremely interesting.
I write now to suggest as worthy of your examination the curious adhesive filaments of mucus emitted by the achenia of many Compositae, of which no doubt you are aware. My attention was first called to the subject by the achenia of an Australian Pumilio (P. argyrolepis), which I briefly described in the "Gardeners' Chronicle," 1861, page 5. As the threads of mucus dry and contract they draw the seeds up into a vertical position on the ground. It subsequently occurred to me that if these seeds were to fall on the wet hairs of any quadruped they would adhere firmly, and might be carried to any distance. I was informed that Decaisne has written a paper on these adhesive threads. What is the meaning of the mucus so copiously emitted from the moistened seeds of Iberis, and of at least some species of Linum? Does the mucus serve as a protection against their being devoured, or as a means of attachment. (707/2. Various theories have been suggested, e.g., that the slime by anchoring the seed to the soil facilitates the entrance of the radicle into the soil: the slime has also been supposed to act as a temporary water-store. See Klebs in Pfeffer's "Untersuchungen aus dem Bot. Inst. zu Tubingen," I., page 581.) I have been prevented reading your paper sooner by attempting to read Dr. Askenasy's pamphlet, but the German is too difficult for me to make it all out. (707/3. E. Askenasy, "Beitrage zur Kritik der Darwin'schen Lehre." Leipzig, 1872.) He seems to follow Nageli completely. I cannot but think that both much underrate the utility of various parts of plants; and that they greatly underrate the unknown laws of correlated growth, which leads to all sorts of modifications, when some one structure or the whole plant is modified for some particular object.
LETTER 708. TO T.H. FARRER. (Lord Farrer).
(708/1. The following letter refers to a series of excellent observations on the fertilisation of Leguminosae, made by Lord Farrer in the autumn of 1869, in ignorance of Delpino's work on the subject. The result was published in "Nature," October 10th and 17th, 1872, and is full of interesting suggestions. The discovery of the mechanism in Coronilla mentioned in a note was one of the cases in which Lord Farrer was forestalled.)
Down {1872}.
I declare I am almost as sorry as if I had been myself forestalled—indeed, more so, for I am used to it. It is, however, a paramount, though bothersome duty in every naturalist to try and make out all that has been done by others on the subject. By all means publish next summer your confirmation and a summary of Delpino's observations, with any new ones of your own. Especially attend about the nectary exterior to the staminal tube. (708/2. This refers to a species of Coronilla in which Lord Farrer made the remarkable discovery that the nectar is secreted on the outside of the calyx. See "Nature," July 2nd, 1874, page 169; also Letter 715.) This will in every way be far better than writing to Delpino. It would not be at all presumptuous in you to criticise Delpino. I am glad you think him so clever; for so it struck me.
Look at hind legs yourself of some humble and hive-bees; in former take a very big individual (if any can be found) for these are the females, the males being smaller, and they have no pollen-collecting apparatus. I do not remember where it is figured—probably in Kirby & Spence—but actual inspection better...
Please do not return any of my books until all are finished, and do not hurry.
I feel certain you will make fine discoveries.
LETTER 709. TO T.H. FARRER. (Lord Farrer). Sevenoaks, October 13th, 1872.
I must send you a line to say how extremely good your article appears to me to be. It is even better than I thought, and I remember thinking it very good. I am particularly glad of the excellent summary of evidence about the common pea, as it will do for me hereafter to quote; nocturnal insects will not do. I suspect that the aboriginal parent had bluish flowers. I have seen several times bees visiting common and sweet peas, and yet varieties, purposely grown close together, hardly ever intercross. This is a point which for years has half driven me mad, and I have discussed it in my "Var. of Animals and Plants under Dom." (709/1. In the second edition (1875) of the "Variation of Animals and Plants," Volume I., page 348, Darwin added, with respect to the rarity of spontaneous crosses in Pisum: "I have reason to believe that this is due to their stignas being prematurely fertilised in this country by pollen from the same flower." This explanation is, we think, almost certainly applicable to Lathyrus odoratus, though in Darwin's latest publication on the subject he gives reasons to the contrary. See "Cross and Self-Fertilisation," page 156, where the problem is left unsolved. Compare Letter 714 to Delpino. In "Life and Letters," III., page 261, the absence of cross-fertilisation is explained as due to want of perfect adaptation between the pea and our native insects. This is Hermann Muller's view: see his "Fertilisation of Flowers," page 214. See Letter 583, note.) I now suspect (and I wish I had strength to experimentise next spring) that from changed climate both species are prematurely fertilised, and therefore hardly ever cross. When artificially crossed by removal of own pollen in bud, the offspring are very vigorous.
Farewell.—I wish I could compel you to go on working at fertilisation instead of so insignificant a subject as the commerce of the country!
You pay me a very pretty compliment at the beginning of your paper.
LETTER 710. TO J.D. HOOKER.
(710/1. The following letters to Sir J.D. Hooker and the late Mr. Moggridge refer to Moggridge's observation that seeds stored in the nest of the ant Atta at Mentone do not germinate, though they are certainly not dead. Moggridge's observations are given in his book, "Harvesting Ants and Trap-Door Spiders," 1873, which is full of interesting details. The book is moreover remarkable in having resuscitated our knowledge of the existence of the seed-storing habit. Mr. Moggridge points out that the ancients were familiar with the facts, and quotes the well-known fable of the ant and the grasshopper, which La Fontaine borrowed from Aesop. Mr. Moggridge (page 5) goes on: "So long as Europe was taught Natural History by southern writers the belief prevailed; but no sooner did the tide begin to turn, and the current of information to flood from north to south, than the story became discredited."
In Moggridge's "supplement" on the same subject, published in 1874, the author gives an account of his experiments made at Darwin's suggestion, and concludes (page 174) that "the vapour of formic acid is incapable of rendering the seeds dormant after the manner of the ants," and that indeed "its influence is always injurious to the seeds, even when present only in excessively minute quantities." Though unable to explain the method employed, he was convinced "that the non-germination of the seeds is due to some direct influence voluntarily exercised by the ants, and not merely to the conditions found in the nest" (page 172). See Volume I., Letter 251.)
Down, February 21st {1873}.
You have given me exactly the information which I wanted.
Geniuses jump. I have just procured formic acid to try whether its vapour or minute drops will delay germination of fresh seeds; trying others at same time for comparison. But I shall not be able to try them till middle of April, as my despotic wife insists on taking a house in London for a month from the middle of March.
I am glad to hear of the Primer (710/2. "Botany" (Macmillan's Science Primers).); it is not at all, I think, a folly. Do you know Asa Gray's child book on the functions of plants, or some such title? It is very good in giving an interest to the subject.
By the way, can you lend me the January number of the "London Journal of Botany" for an article on insect-agency in fertilisation?
LETTER 711. TO J. TRAHERNE MOGGRIDGE. Down, August 27th, 1873.
I thank you for your very interesting letter, and I honour you for your laborious and careful experiments. No one knows till he tries how many unexpected obstacles arise in subjecting plants to experiments.
I can think of no suggestions to make; but I may just mention that I had intended to try the effects of touching the dampened seeds with the minutest drop of formic acid at the end of a sharp glass rod, so as to imitate the possible action of the sting of the ant. I heartily hope that you may be rewarded by coming to some definite result; but I fail five times out of six in my own experiments. I have lately been trying some with poor success, and suppose that I have done too much, for I have been completely knocked up for some days.
LETTER 712. TO J. TRAHERNE MOGGRIDGE. Down, March 10th, 1874.
I am very sorry to hear that the vapour experiments have failed; but nothing could be better, as it seems to me, than your plan of enclosing a number of the ants with the seeds. The incidental results on the power of different vapours in killing seeds and stopping germination appear very curious, and as far as I know are quite new.
P.S.—I never before heard of seeds not germinating except during a certain season; it will be a very strange fact if you can prove this. (712/1. Certain seeds pass through a resting period before germination. See Pfeffer's "Pflanzenphysiologie," Edition I., Volume II., page III.)
LETTER 713. TO H. MULLER. Down, May 30th, 1873.
I am much obliged for your letter received this morning. I write now chiefly to give myself the pleasure of telling you how cordially I admire the last part of your book, which I have finished. (713/1. "Die Befruchtung der Blumen durch Insekten": Leipzig, 1873. An English translation was published in 1883 by Prof. D'Arcy Thompson. The "Prefatory Notice" to this work (February 6th, 1882) is almost the last of Mr. Darwin's writings. See "Life and Letters," page 281.) The whole discussion seems to me quite excellent, and it has pleased me not a little to find that in the rough MS. of my last chapter I have arrived on many points at nearly the same conclusions that you have done, though we have reached them by different routes. (713/2. "The Effects of Cross and Self-Fertilisation in the Vegetable Kingdom": London, 1876.)
LETTER 714. TO F. DELPINO. Down, June 25th {1873}.
I thank you sincerely for your letter. I am very glad to hear about Lathyrus odoratus, for here in England the vars. never cross, and yet are sometimes visited by bees. (714/1. In "Cross and Self-Fertilisation," page 156, Darwin quotes the information received from Delpino and referred to in the present letter—namely, that it is the fixed opinion of the Italian gardeners that the varieties do intercross. See Letter 709.) Pisum sativum I have also many times seen visited by Bombus. I believe the cause of the many vars. not crossing is that under our climate the flowers are self-fertilised at an early period, before the corolla is fully expanded. I shall examine this point with L. odoratus. I have read H. Muller's book, and it seems to me very good. Your criticism had not occurred to me, but is, I think just—viz. that it is much more important to know what insects habitually visit any flower than the various kinds which occasionally visit it. Have you seen A. Kerner's book "Schutzmittel des Pollens," 1873, Innsbruck. (714/2. Afterwards translated by Dr. Ogle as "Flowers and their Unbidden Guests," with a prefatory letter by Charles Darwin, 1878.) It is very interesting, but he does not seem to know anything about the work of other authors.
I have Bentham's paper in my house, but have not yet had time to read a word of it. He is a man with very sound judgment, and fully admits the principle of evolution.
I have lately had occasion to look over again your discussion on anemophilous plants, and I have again felt much admiration at your work. (714/3. "Atti della Soc. Italiana di Scienze Nat." Volume XIII.)
(714/4. In the beginning of August, 1873, Darwin paid the first of several visits to Lord Farrer's house at Abinger. When sending copies of Darwin's letters for the "Life and Letters," Lord Farrer was good enough to add explanatory notes and recollections, from which we quote the following sketch.)
"Above my house are some low hills, standing up in the valley, below the chalk range on the one hand and the more distant range of Leith Hill on the other, with pretty views of the valley towards Dorking in one direction and Guildford in the other. They are composed of the less fertile Greensand strata, and are covered with fern, broom, gorse, and heath. Here it was a particular pleasure of his to wander, and his tall figure, with his broad-brimmed Panama hat and long stick like an alpenstock, sauntering solitary and slow over our favourite walks, is one of the pleasantest of the many pleasant associations I have with the place."
LETTER 715. TO T.H. FARRER (Lord Farrer).
(715/1. The following note by Lord Farrer explains the main point of the letter, which, however, refers to the "bloom" problem as well as to Coronilla:—
"I thought I had found out what puzzled us in Coronilla varia: in most of the Papilionaceae, when the tenth stamen is free, there is nectar in the staminal tube, and the opening caused by the free stamen enables the bee to reach the nectar, and in so doing the bee fertilises the plant. In Coronilla varia, and in several other species of Coronilla, there is no nectar in the staminal tube or in the tube of the corolla. But there are peculiar glands with nectar on the outside of the calyx, and peculiar openings in the tube of the corolla through which the proboscis of the bee, whilst entering the flower in the usual way and dusting itself with pollen, can reach these glands, thus fertilising the plant in getting the nectar. On writing this to Mr. Darwin, I received the following characteristic note.
The first postscript relates to the rough ground behind my house, over which he was fond of strolling. It had been ploughed up and then allowed to go back, and the interest was to watch how the numerous species of weeds of cultivation which followed the plough gradually gave way in the struggle for existence to the well-known and much less varied flora of an English common.")
Bassett, Southampton, August 14th, 1873.
You are the man to conquer a Coronilla. (715/2. In a former letter to Lord Farrer, Darwin wrote: "Here is a maxim for you, 'It is disgraceful to be beaten by a Coronilla.'") I have been looking at the half-dried flowers, and am prepared to swear that you have solved the mystery. The difference in the size of the cells on the calyx under the vexillum right down to the common peduncle is conspicuous. The flour still adhered to this side; I see little bracteae or stipules apparently with glandular ends at the base of the calyces. Do these secrete? It seems to me a beautiful case. When I saw the odd shape of the base of the vexillum, I concluded that it must have some meaning, but little dreamt what that was. Now there remains only the one serious point—viz.the separation of the one stamen. I daresay that you are right in that nectar was originally secreted within the staminal tube; but why has not the one stamen long since cohered? The great difference in structure for fertilisation within the same genus makes one believe that all such points are vary variable. (715/3. Coronilla emerus is of the ordinary papilionaceous type.) With respect to the non-coherence of the one stamen, do examine some flower-buds at a very early age; for parts which are largely developed are often developed to an unusual degree at a very early age, and it seems to me quite possible that the base of the vexillum (to which the single stamen adhered) might thus be developed, and thus keep it separate for a time from the other stamens. The cohering stamens to the right and left of the single one seem to me to be pushed out a little laterally. When you have finished your observations, you really ought to send an account with a diagram to "Nature," recalling your generalisation about the diadelphous structure, and now explaining the exception of Coronilla. (715/4. The observations were published in "Nature," Volume X., 1874, page 169.)
Do add a remark how almost every detail of structure has a meaning where a flower is well examined.
Your observations pleased me so much that I could not sit still for half an hour.
Please to thank Mr. Payne (715/5. Lord Farrer's gardener.) for his remarks, which are of value to me, with reference to Mimosa. I am very much in doubt whether opening the sashes can act by favouring the evaporation of the drops; may not the movement of the leaves shake off the drops, or change their places? If Mr. Payne remembers any plant which is easily injured by drops, I wish he would put a drop or two on a leaf on a bright day, and cover the plant with a clean bell-glass, and do the same for another plant, but without a bell-glass over it, and observe the effects.
Thank you much for wishing to see us again at Abinger, and it is very doubtful whether it will be Coronilla, Mr. Payne, the new garden, the children, E. {Lady Farrer}, or yourself which will give me the most pleasure to see again.
P.S. 1.—It will be curious to note in how many years the rough ground becomes quite uniform in its flora.
P.S. 2.—One may feel sure that periodically nectar was secreted within the flower and then secreted by the calyx, as in some species of Iris and orchids. This latter being taken advantage of in Coronilla would allow of the secretion within the flower ceasing, and as this change was going on in the two secretions, all the parts of the flower would become modified and correlated.
LETTER 716. TO J. BURDON SANDERSON. Down, Tuesday, September 9th {1873}.
(716/1. Sir J. Burdon Sanderson showed that in Dionoea movement is accompanied by electric disturbances closely analogous to those occurring in muscle (see "Nature," 1874, pages 105, 127; "Proc. R. Soc." XXI., and "Phil. Trans." Volume CLXXIII., 1883, where the results are finally discussed).)
I will send up early to-morrow two plants {of Dionoea} with five goodish leaves, which you will know by their being tied to sticks. Please remember that the slightest touch, even by a hair, of the three filaments on each lobe makes the leaf close, and it will not open for twenty-four hours. You had better put 1/4 in. of water into the saucers of the pots. The plants have been kept too cool in order to retard them. You had better keep them rather warm (i.e. temperature of warm greenhouse) for a day, and in a good light.
I am extremely glad you have undertaken this subject. If you get a positive result, I should think you ought to publish it separately, and I could quote it; or I should be most glad to introduce any note by you into my account.
I have no idea whether it is troublesome to try with the thermo-electric pile any change of temperature when the leaf closes. I could detect none with a common thermometer. But if there is any change of temperature I should expect it would occur some eight to twelve or twenty-four hours after the leaf has been given a big smashed fly, and when it is copiously secreting its acid digestive fluid.
I forgot to say that, as far as I can make out, the inferior surface of the leaf is always in a state of tension, and that the contraction is confined to the upper surface; so that when this contraction ceases or suddenly fails (as by immersion in boiling water) the leaf opens again, or more widely than is natural to it.
Whenever you have quite finished, I will send for the plants in their basket. My son Frank is staying at 6, Queen Anne Street, and comes home on Saturday afternoon, but you will not have finished by that time.
P.S. I have repeated my experiment on digestion in Drosera with complete success. By giving leaves a very little weak hydrochloric acid, I can make them digest albumen—i.e. white of egg—quicker than they can do naturally. I most heartily thank you for all your kindness. I have been pretty bad lately, and must work very little.
LETTER 717. TO J. BURDON SANDERSON. September 13th {1873}.
How very kind it was of you to telegraph to me. I am quite delighted that you have got a decided result. Is it not a very remarkable fact? It seems so to me, in my ignorance. I wish I could remember more distinctly what I formerly read of Du Bois Raymond's results. My poor memory never serves me for more than a vague guide. I really think you ought to try Drosera. In a weak solution of phosphate of ammonia (viz. 1 gr. to 20 oz. of water) it will contract in about five minutes, and even more quickly in pure warm water; but then water, I suppose, would prevent your trial. I forget, but I think it contracts pretty quickly (i.e. in an hour or two) with a large drop of a rather stronger solution of the phosphate, or with an atom of raw meat on the disc of the leaf.
LETTER 718. TO J.D. HOOKER. October 31st, 1873.
Now I want to tell you, for my own pleasure, about the movements of Desmodium.
1. When the plant goes to sleep, the terminal leaflets hang vertically down, but the petioles move up towards the axis, so that the dependent leaves are all crowded round it. The little leaflets never go to sleep, and this seems to me very odd; they are at their games of play as late as 11 o'clock at night and probably later. (718/1. Stahl ("Botanische Zeitung," 1897, page 97) has suggested that the movements of the dwarf leaflets in Desmodium serve to shake the large terminal leaflets, and thus increase transpiration. According to Stahl's view their movement would be more useful at night than by day, because stagnation of the transpiration-current is more likely to occur at night.)
2. If the plant is shaken or syringed with tepid water, the terminal leaflets move down through about an angle of 45 deg, and the petioles likewise move about 11 deg downwards; so that they move in an opposite direction to what they do when they go to sleep. Cold water or air produces the same effect as does shaking. The little leaflets are not in the least affected by the plant being shaken or syringed. I have no doubt, from various facts, that the downward movement of the terminal leaflets and petioles from shaking and syringing is to save them from injury from warm rain.
3. The axis, the main petiole, and the terminal leaflets are all, when the temperature is high, in constant movement, just like that of climbing plants. This movement seems to be of no service, any more than the incessant movement of amoeboid bodies. The movement of the terminal leaflets, though insensible to the eye, is exactly the same as that of the little lateral leaflets—viz. from side to side, up and down, and half round their own axes. The only difference is that the little leaflets move to a much greater extent, and perhaps more rapidly; and they are excited into movement by warm water, which is not the case with the terminal leaflet. Why the little leaflets, which are rudimentary in size and have lost their sleep-movements and their movements from being shaken, should not only have retained, but have their spontaneous movements exaggerated, I cannot conceive. It is hardly credible that it is a case of compensation. All this makes me very anxious to examine some plant (if possible one of the Leguminosae) with either the terminal or lateral leaflets greatly reduced in size, in comparison with the other leaflets on the same leaf. Can you or any of your colleagues think of any such plant? It is indirectly on this account that I so much want the seeds of Lathyrus nissolia.
I hear from Frank that you think that the absence of both lateral leaflets, or of one alone, is due to their having dropped off; I thought so at first, and examined extremely young leaves from the tips of the shoots, and some of them presented the same characters. Some appearances make me think that they abort by becoming confluent with the main petiole.
I hear also that you doubt about the little leaflets ever standing not opposite to each other: pray look at the enclosed old leaf which has been for a time in spirits, and can you call the little leaflets opposite? I have seen many such cases on both my plants, though few so well marked.
LETTER 719. TO J.D. HOOKER. Down, October 23rd {1873}.
How good you have been about the plants; but indeed I did not intend you to write about Drosophyllum, though I shall be very glad to have a specimen. Experiments on other plants lead to fresh experiments. Neptunia is evidently a hopeless case. I shall be very glad of the other plants whenever they are ready. I constantly fear that I shall become to you a giant of bores.
I am delighted to hear that you are at work on Nepenthes, and I hope that you will have good luck. It is good news that the fluid is acid; you ought to collect a good lot and have the acid analysed. I hope that the work will give you as much pleasure as analogous work has me. (719/1. Hooker's work on Nepenthes is referred to in "Insectivorous Plants," page 97: see also his address at the Belfast meeting of the British Association, 1874.) I do not think any discovery gave me more pleasure than proving a true act of digestion in Drosera.
LETTER 720. TO J.D. HOOKER. Down, November 24th, 1873.
I have been greatly interested by Mimosa albida, on which I have been working hard. Whilst your memory is pretty fresh, I want to ask a question. When this plant was most sensitive, and you irritated it, did the opposite leaflets shut up quite close, as occurs during sleep, when even a lancet could not be inserted between the leaflets? I can never cause the leaflets to come into contact, and some reasons make me doubt whether they ever do so except during sleep; and this makes me wish much to hear from you. I grieve to say that the plant looks more unhealthy, even, than it was at Kew. I have nursed it like the tenderest infant; but I was forced to cut off one leaf to try the bloom, and one was broken by the manner of packing. I have never syringed (with tepid water) more than one leaf per day; but if it dies, I shall feel like a murderer. I am pretty well convinced that I shall make out my case of movements as a protection against rain lodging on the leaves. As far as I have as yet made out, M. albida is a splendid case.
I have had no time to examine more than one species of Eucalyptus. The seedlings of Lathyrus nissolia are very interesting to me; and there is something wonderful about them, unless seeds of two distinct leguminous species have got somehow mingled together.
LETTER 721. TO W. THISELTON-DYER. Down, December 4th, 1873.
As Hooker is so busy, I should be very much obliged if you could give me the name of the enclosed poor specimen of Cassia. I want much to know its name, as its power of movement, when it goes to sleep, is very remarkable. Linnaeus, I find, was aware of this. It twists each separate leaflet almost completely round (721/1. See "Power of Movement in Plants," Figure 154, page 370.), so that the lower surface faces the sky, at the same time depressing them all. The terminal leaflets are pointed towards the base of the leaf. The whole leaf is also raised up about 12 deg. When I saw that it possessed such complex powers of movement, I thought it would utilise its power to protect the leaflets from rain. Accordingly I syringed the plant for two minutes, and it was really beautiful to see how each leaflet on the younger leaves twisted its short sub-petiole, so that the blade was immediately directed at an angle between 45 and 90 deg to the horizon. I could not resist the pleasure of just telling you why I want to know the name of the Cassia. I should add that it is a greenhouse plant. I suppose that there will not be any better flowers till next summer or autumn.
LETTER 722. TO T. BELT.
(722/1. Belt's account, discussed in this letter, is probably that published in his "Naturalist in Nicaragua" (1874), where he describes "the relation between the presence of honey-secreting glands on plants, and the protection to the latter secured by the attendance of ants attracted by the honey." (Op. cit., pages 222 et seq.))
Thursday {1874?}.
Your account of the ants and their relations seems to me to possess extraordinary interest. I do not doubt that the excretion of sweet fluid by the glands is in your cases of great advantage to the plants by means of the ants, but I cannot avoid believing that primordially it is a simple excretion, as occasionally occurs from the surface of the leaves of lime trees. It is quite possible that the primordial excretion may have been beneficially increased to serve the plant. In the common laurel {Prunus laurocerasus} of our gardens the hive-bees visit incessantly the glands of the young leaves, on their under sides; and I should altogether doubt whether their visits or the occasional visits of ants was of any service to the laurel. The stipules of the common vetch secrete largely during sunshine, and hive-bees collect the sweet fluid. So I think it is with the common bean.
I am writing this away from home, and I have come away to get some rest, having been a good deal overworked. I shall read your book with great interest when published, but will not trouble you to send the MS., as I really have no spare strength or time. I believe that your book, judging by the chapter sent, will be extremely valuable.
LETTER 723. TO J.D. HOOKER.
(723/1. The following letter refers to Darwin's prediction as to the manner in which Hedychium (Zinziberaceae) is fertilised. Sir J.D. Hooker seems to have made inquiries in India in consequence of which Darwin received specimens of the moth which there visits the flower, unfortunately so much broken as to be useless (see "Life and Letters," III., page 284).)
Down, March 25th {1874}.
I am glad to hear about the Hedychium, and how soon you have got an answer! I hope that the wings of the Sphinx will hereafter prove to be bedaubed with pollen, for the case will then prove a fine bit of prophecy from the structure of a flower to special and new means of fertilisation.
By the way, I suppose you have noticed what a grand appearance the plant makes when the green capsules open, and display the orange and crimson seeds and interior, so as to attract birds, like the pale buff flowers to attract dusk-flying lepidoptera. I presume you do not want seeds of this plant, as I have plenty from artificial fertilisation.
(723/2. In "Nature," June 22nd, 1876, page 173, Hermann Muller communicated F. Muller's observation on the fertilisation of a bright-red-flowered species of Hedychium, which is visited by Callidryas, chiefly the males of C. Philea. The pollen is carried by the tips of the butterfly's wing, to which it is temporarily fixed by the slimy layer produced by the degeneration of the anther-wall.
LETTER 724. TO W. THISELTON-DYER. Down, June 4th {1874}.
I am greatly obliged to you about the Opuntia, and shall be glad if you can remember Catalpa. I wish some facts on the action of water, because I have been so surprised at a stream not acting on Dionoea and Drosera. (724/1. See Pfeffer, "Untersuchungen Bot. Inst. zu Tubingen," Bd. I., 1885, page 518. Pfeffer shows that in some cases—Drosera, for instance—water produces movement only when it contains fine particles in suspension. According to Pfeffer the stamens of Berberis, and the stigma of Mimulus, are both stimulated by gelatine, the action of which is, generally speaking, equivalent to that of water.) Water does not act on the stamens of Berberis, but it does on the stigma of Mimulus. It causes the flowers of the bedding-out Mesembryanthemum and Drosera to close, but it has not this effect on Gazania and the daisy, so I can make out no rule.
I hope you are going on with Nepenthes; and if so, you will perhaps like to hear that I have just found out that Pinguicula can digest albumen, gelatine, etc. If a bit of glass or wood is placed on a leaf, the secretion is not increased; but if an insect or animal-matter is thus placed, the secretion is greatly increased and becomes feebly acid, which was not the case before. I have been astonished and much disturbed by finding that cabbage seeds excite a copious secretion, and am now endeavouring to discover what this means. (724/2. Clearly it had not occurred to Darwin that seeds may supply nitrogenous food as well as insects: see "Insectivorous Plants," page 390.) Probably in a few days' time I shall have to beg a little information from you, so I will write no more now.
P.S. I heard from Asa Gray a week ago, and he tells me a beautiful fact: not only does the lid of Sarracenia secrete a sweet fluid, but there is a line or trail of sweet exudation down to the ground so as to tempt insects up. (724/3. A dried specimen of Sarracenia, stuffed with cotton wool, was sometimes brought from his study by Mr. Darwin, and made the subject of a little lecture to visitors of natural history tastes.)
LETTER 725. TO W. THISELTON-DYER. Down, June 23rd, 1874.
I wrote to you about a week ago, thanking you for information on cabbage seeds, asking you the name of Luzula or Carex, and on some other points; and I hope before very long to receive an answer. You must now, if you can, forgive me for being very troublesome, for I am in that state in which I would sacrifice friend or foe. I have ascertained that bits of certain leaves, for instance spinach, excite much secretion in Pinguicula, and that the glands absorb matter from the leaves. Now this morning I have received a lot of leaves from my future daughter-in-law in North Wales, having a surprising number of captured insects on them, a good many leaves, and two seed-capsules. She informs me that the little leaves had excited secretion; and my son and I have ascertained this morning that the protoplasm in the glands beneath the little leaves has undoubtedly undergone aggregation. Therefore, absurd as it may sound, I am prepared to affirm that Pinguicula is not only insectivorous, but graminivorous, and granivorous! Now I want to beg you to look under the simple microscope at the enclosed leaves and seeds, and, if you possibly can, tell me their genera. The little narrow leaves are remarkable (725/1. Those of Erica tetralix.); they are fleshy, with the edges much curled from the axis of the plant, and bear a few long glandular hairs; these grow in little tufts. These are the commonest in Pinguicula, and seem to afford most nutritious matter. A second leaf is like a miniature sycamore. With respect to the seeds, I suppose that one is a Carex; the other looks like that of Rumex, but is enclosed in a globular capsule. The Pinguicula grew on marshy, low, mountainous land.
I hope you will think this subject sufficiently interesting to make you willing to aid me as far as you can. Anyhow, forgive me for being so very troublesome.
LETTER 726. TO J.D. HOOKER. Down, August 30th {1874}.
I am particularly obliged for your address. (726/1. Presidential address (Biological Section) at the Belfast meeting of the British Association, 1874.) It strikes me as quite excellent, and has interested me in the highest degree. Nor is this due to my having worked at the subject, for I feel sure that I should have been just as much struck, perhaps more so, if I had known nothing about it. You could not, in my opinion, have put the case better. There are several lights (besides the facts) in your essay new to me, and you have greatly honoured me. I heartily congratulate you on so splendid a piece of work. There is a misprint at page 7, Mitschke for Nitschke. There is a partial error at page 8, where you say that Drosera is nearly indifferent to organic substances. This is much too strong, though they do act less efficiently than organic with soluble nitrogenous matter; but the chief difference is in the widely different period of subsequent re-expansion. Thirdly, I did not suggest to Sanderson his electrical experiments, though, no doubt, my remarks led to his thinking of them.
Now for your letter: you are very generous about Dionoea, but some of my experiments will require cutting off leaves, and therefore injuring plants. I could not write to Lady Dorothy {Nevill}. Rollisson says that they expect soon a lot from America. If Dionoea is not despatched, have marked on address, "to be forwarded by foot-messenger."
Mrs. Barber's paper is very curious, and ought to be published (726/2. Mrs. Barber's paper on the pupa of Papilio Nireus assuming different tints corresponding to the objects to which it was attached, was communicated by Mr. Darwin to the "Trans. Entomolog. Soc." 1874.); but when you come here (and REMEMBER YOU OFFERED TO COME) we will consult where to send it. Let me hear when you recommence on Cephalotus or Sarracenia, as I think I am now on right track about Utricularia, after wasting several weeks in fruitless trials and observations. The negative work takes five times more time than the positive.
LETTER 727. TO J.D. HOOKER. Down, September 18th {1874}.
I have had a splendid day's work, and must tell you about it.
Lady Dorothy sent me a young plant of U{tricularia} montana (727/1. See "Life and Letters," III., page 327, and "Insectivorous Plants," page 431.), which I fancy is the species you told me of. The roots or rhizomes (for I know not which they are; I can see no scales or internodes or absorbent hairs) bear scores of bladders from 1/20 to 1/100 of an inch in diameter; and I traced these roots to the depth of 1 1/2 in. in the peat and sand. The bladders are like glass, and have the same essential structure as those of our species, with the exception that many exterior parts are aborted. Internally the structure is perfect, as is the minute valvular opening into the bladder, which is filled with water. I then felt sure that they captured subterranean insects, and after a time I found two with decayed remnants, with clear proof that something had been absorbed, which had generated protoplasm. When you are here I shall be very curious to know whether they are roots or rhizomes.
Besides the bladders there are great tuber-like swellings on the rhizomes; one was an inch in length and half in breadth. I suppose these must have been described. I strongly suspect that they serve as reservoirs for water. (727/2. The existence of water-stores is quite in accordance with the epiphytic habit of the plant.) But I shall experimentise on this head. A thin slice is a beautiful object, and looks like coarsely reticulated glass.
If you have an old plant which could be turned out of its pot (and can spare the time), it would be a great gain to me if you would tear off a bit of the roots near the bottom, and shake them well in water, and see whether they bear these minute glass-like bladders. I should also much like to know whether old plants bear the solid bladder-like bodies near the upper surface of the pot. These bodies are evidently enlargements of the roots or rhizomes. You must forgive this long letter, and make allowance for my delight at finding this new sub-group of insect-catchers. Sir E. Tennent speaks of an aquatic species of Utricularia in Ceylon, which has bladders on its roots, and rises annually to the surface, as he says, by this means. (727/3. Utricularia stellaris. Emerson Tennent's "Ceylon," Volume I., page 124, 1859.)
We shall be delighted to see you here on the 26th; if you will let us know your train we will send to meet you. You will have to work like a slave while you are here.
LETTER 728. TO J. JENNER WEIR.
(728/1. In 1870 Mr. Jenner Weir wrote to Darwin: "My brother has but two kinds of laburnum, viz., Cytisus purpureus, very erect, and Cytisus alpinus, very pendulous. He has several stocks of the latter grafted with the purple one; and this year, the grafts being two years old, I saw in one, fairly above the stock, about four inches, a raceme of purely yellow flowers with the usual dark markings, and above them a bunch of purely purple flowers; the branches of the graft in no way showed an intermediate character, but had the usual rigid growth of purpureus."
Early in July 1875, when Darwin was correcting a new edition of "Variation under Domestication," he again corresponded with Mr. Weir on the subject.)
Down, July 8th {1875}.
I thank you cordially. The case interests me in a higher degree than anything which I have heard for a very long time. Is it your brother Harrison W., whom I know? I should like to hear where the garden is. There is one other very important point which I am most anxious to hear—viz., the nature of the leaves at the base of the yellow racemes, for leaves are always there produced with the yellow laburnums, and I suppose so in the case of C. purpureus. As the tree has produced yellow racemes several times, do you think you could ask your brother to cut off and send me by post in a box a small branch of the purple stock with the pods or leaves of the yellow sport? (728/2. "The purple stock" here means the supposed C. purpureus, on which a yellow-flowered branch was borne.) This would be an immense favour, for then I would cut the point of junction longitudinally and examine slice under the microscope, to be able to state no trace of bud of yellow kind having been inserted. I do not suspect anything of the kind, but it is sure to be said that your brother's gardener, either by accident or fraud, inserted a bud. Under this point of view it would be very good to gather from your brother how many times the yellow sport has appeared. The case appears to me so very important as to be worth any trouble. Very many thanks for all assistance so kindly given.
I will of course send a copy of new edition of "Variation under Domestication" when published in the autumn.
LETTER 729. TO J. JENNER WEIR.
(729/1. On July 9th Mr. Weir wrote to say that a branch of the Cytisus had been despatched to Down. The present letter was doubtless written after Darwin had examined the specimen. In "Variation under Domestication," Edition II., Volume I., page 417, note, he gives for a case recorded in the "Gardeners' Chronicle" in 1857 the explanation here offered (viz. that the graft was not C. purpureus but C. Adami), and adds, "I have ascertained that this occurred in another instance." This second instance is doubtless Mr. Weir's.)
Down, July 10th, 1875.
I do not know how to thank you enough; pray give also my thanks and kind remembrances to your brother. I am sure you will forgive my expressing my doubts freely, as I well know that you desire the truth more than anything else. I cannot avoid the belief that some nurseryman has sold C{ytisus} Adami to your brother in place of the true C. purpureus. The latter is a little bush only 3 feet high (Loudon), and when I read your account, it seemed to me a physical impossibility that a sporting branch of C. alpinus could grow to any size and be supported on the extremely delicate branches of C. purpureus. If I understand rightly your letter, you consider the tuft of small shoots on one side of the sporting C. alpinus from Weirleigh as C. purpureus; but these shoots are certainly those of C. Adami. I earnestly beg you to look at the specimens enclosed. The branch of the true C. purpureus is the largest which I could find. If C. Adami was sold to your brother as C. purpureus, everything is explained; for then the gardener has grafted C. Adami on C. alpinus, and the former has sported in the usual manner; but has not sported into C. purpureus, only into C. alpinus. C. Adami does not sport less frequently into C. purpureus than into C. alpinus. Are the purple flowers borne on moderately long racemes? If so, the plant is certainly C. Adami, for the true C. purpureus bears flowers close to the branches. I am very sorry to be so troublesome, but I am very anxious to hear again from you.
C. purpureus bears "flowers axillary, solitary, stalked."
P.S.—I think you said that the purple {tree} at Weirleigh does not seed, whereas the C. purpureus seeds freely, as you may see in enclosed. C. Adami never produces seeds or pods.
LETTER 730. TO E. HACKEL.
(730/1. The following extract refers to Darwin's book on "Cross and Self-Fertilisation.")
November 13th, 1875.
I am now busy in drawing up an account of ten years' experiments in the growth and fertility of plants raised from crossed and self-fertilised flowers. It is really wonderful what an effect pollen from a distinct seedling plant, which has been exposed to different conditions of life, has on the offspring in comparison with pollen from the same flower or from a distinct individual, but which has been long subjected to the same conditions. The subject bears on the very principle of life, which seems almost to require changes in the conditions.
LETTER 731. TO G.J. ROMANES.
(731/1. The following extract from a letter to Romanes refers to Francis Darwin's paper, "Experiments on the Nutrition of Drosera rotundifolia." "Linn. Soc. Journ." {1878}, published 1880, page 17.)
August 9th {1876}.
The second point which delights me, seeing that half a score of botanists throughout Europe have published that the digestion of meat by plants is of no use to them (a mere pathological phenomenon, as one man says!), is that Frank has been feeding under exactly similar conditions a large number of plants of Drosera, and the effect is wonderful. On the fed side the leaves are much larger, differently coloured, and more numerous; flower-stalks taller and more numerous, and I believe far more seed capsules,—but these not yet counted. It is particularly interesting that the leaves fed on meat contain very many more starch granules (no doubt owing to more protoplasm being first formed); so that sections stained with iodine, of fed and unfed leaves, are to the naked eye of very different colours.
There, I have boasted to my heart's content, and do you do the same, and tell me what you have been doing.
LETTER 732. TO J.D. HOOKER. Down, October 25th {1876}.
If you can put the following request into any one's hands pray do so; but if not, ignore my request, as I know how busy you are.
I want any and all plants of Hoya examined to see if any imperfect flowers like the one enclosed can be found, and if so to send them to me, per post, damp. But I especially want them as young as possible.
They are very curious. I have examined some sent me from Abinger (732/1. Lord Farrer's house.), but they were a month or two too old, and every trace of pollen and anthers had disappeared or had never been developed. Yet a very fine pod with apparently good seed had been formed by one such flower. (732/2. The seeds did not germinate; see the account of Hoya carnosa in "Forms of Flowers," page 331.)
LETTER 733. TO G.J. ROMANES.
(733/1. Published in the "Life of Romanes," page 62.)
Down, August 10th {1877}.
When I went yesterday I had not received to-day's "Nature," and I thought that your lecture was finished. (733/2. Abstract of a lecture on "Evolution of Nerves and Nervo-Systems," delivered at the Royal Institution, May 25th, 1877. "Nature," July 19th, August 2nd, August 9th, 1877.) This final part is one of the grandest essays which I ever read.
It was very foolish of me to demur to your lines of conveyance like the threads in muslin (733/3. "Nature," August 2nd, page 271.), knowing how you have considered the subject: but still I must confess I cannot feel quite easy. Everyone, I suppose, thinks on what he has himself seen, and with Drosera, a bit of meat put on any one gland on its disc causes all the surrounding tentacles to bend to this point, and here there can hardly be differentiated lines of conveyance. It seems to me that the tentacles probably bend to that point wherever a molecular wave strikes them, which passes through the cellular tissue with equal ease in all directions in this particular case. (733/4. Speaking generally, the transmission takes place more readily in the longitudinal direction than across the leaf: see "Insectivorous Plants," page 239.) But what a fine case that of the Aurelia is! (733/5. Aurelia aurita, one of the medusae. "Nature," pages 269-71.)
LETTER 734. TO W. THISELTON-DYER. 6, Queen Anne Street {December 1876}.
Tell Hooker I feel greatly aggrieved by him: I went to the Royal Society to see him for once in the chair of the Royal, to admire his dignity and enjoy it, and lo and behold, he was not there. My outing gave me much satisfaction, and I was particularly glad to see Mr. Bentham, and to see him looking so wonderfully well and young. I saw lots of people, and it has not done me a penny's worth of harm, though I could not get to sleep till nearly four o'clock.
LETTER 735. TO D. OLIVER. Down, October, 13th {1876?}.
You must be a clair-voyant or something of that kind to have sent me such useful plants. Twenty-five years ago I described in my father's garden two forms of Linum flavum (thinking it a case of mere variation); from that day to this I have several times looked, but never saw the second form till it arrived from Kew. Virtue is never its own reward: I took paper this summer to write to you to ask you to send me flowers, {so} that I might beg plants of this Linum, if you had the other form, and refrained, from not wishing to trouble you. But I am now sorry I did, for I have hardly any doubt that L. flavum never seeds in any garden that I have seen, because one form alone is cultivated by slips. (735/1. Id est, because, the plant being grown from slips, one form alone usually occurs in any one garden. It is also arguable that it is grown by slips because only one form is common, and therefore seedlings cannot be raised.)
(736/1. The following five letters refer to Darwin's work on "bloom"—a subject on which he did not live to complete his researches:—
One of his earliest letters on this subject was addressed in August, 1873, to Sir Joseph Hooker (736/2. Published in "Life and Letters," III., page 339.):
"I want a little information from you, and if you do not yourself know, please to enquire of some of the wise men of Kew.
"Why are the leaves and fruit of so many plants protected by a thin layer of waxy matter (like the common cabbage), or with fine hair, so that when such leaves or fruit are immersed in water they appear as if encased in thin glass? It is really a pretty sight to put a pod of the common pea, or a raspberry, into water. I find several leaves are thus protected on the under surface and not on the upper.
"How can water injure the leaves, if indeed this is at all the case?"
On this latter point Darwin wrote to the late Lord Farrer:
"I am now become mad about drops of water injuring leaves. Please ask Mr. Payne (736/3. Lord Farrer's gardener.) whether he believes, FROM HIS OWN EXPERIENCE, that drops of water injure leaves or fruit in his conservatories. It is said that the drops act as burning-glasses; if this is true, they would not be at all injurious on cloudy days. As he is so acute a man, I should very much like to hear his opinion. I remember when I grew hothouse orchids I was cautioned not to wet their leaves; but I never then thought on the subject."
The next letter, though of later date than some which follow it, is printed here because it briefly sums his results and serves as guide to the letters dealing with the subject.)
LETTER 736. TO W. THISELTON-DYER.
(736/4. Published in "Life and Letters," III., page 341.)
Down, September 5th {1877}.
One word to thank you. I declare, had it not been for your kindness, we should have broken down. As it is we have made out clearly that with some plants (chiefly succulent) the bloom checks evaporation—with some certainly prevents attacks of insects; with SOME sea-shore plants prevents injury from salt water, and, I believe, with a few prevents injury from pure water resting on the leaves. This latter is as yet the most doubtful and the most interesting point in relation to the movements of plants.
(736/5. Modern research, especially that of Stahl on transpiration ("Bot. Zeitung," 1897, page 71) has shown that the question is more complex than it appeared in 1877. Stahl's point of view is that moisture remaining on a leaf checks the transpiration-current; and by thus diminishing the flow of mineral nutriment interferes with the process of assimilation. Stahl's idea is doubtless applicable to the whole problem of bloom on leaves. For other references to bloom see letters 685, 689 and 693.)
LETTER 737. TO J.D. HOOKER. Down, August 19th, 1873.
The next time you walk round the garden ask Mr. Smith (737/1. Probably John Smith (1798-1888), for some years Curator, Royal Gardens, Kew.), or any of your best men, what they think about injury from watering during sunshine. One of your men—viz., Mr. Payne, at Abinger, who seems very acute—declares that you may water safely any plant out of doors in sunshine, and that you may do the same for plants under glass if the sashes are opened. This seems to me very odd, but he seems positive on the point, and acts on it in raising splendid grapes. Another good gardener maintains that it is only COLD water dripping often on the same point of a leaf that ever injures it. I am utterly perplexed, but interested on the point. Give me what you learn when you come to Down.
I should like to hear what plants are believed to be most injured by being watered in sunshine, so that I might get such.
I expect that I shall be utterly beaten, as on so many other points; but I intend to make a few experiments and observations. I have already convinced myself that drops of water do NOT act as burning lenses.
LETTER 738. TO J.D. HOOKER. December 20th {1873}.
I find that it is no use going on with my experiments on the evil effects of water on bloom-divested leaves. Either I erred in the early autumn or summer in some incomprehensible manner, or, as I suspect to be the case, water is only injurious to leaves when there is a good supply of actinic rays. I cannot believe that I am all in the wrong about the movements of the leaves to shoot off water.
The upshot of all this is that I want to keep all the plants from Kew until the spring or early summer, as it is mere waste of time going on at present.
LETTER 739. TO W. THISELTON-DYER. Down, July 22nd {1877}.
Many thanks for seeds of the Malva and information about Averrhoa, which I perceived was sensitive, as A. carambola is said to be; and about Mimosa sensitiva. The log-wood {Haematoxylon} has interested me much. The wax is very easily removed, especially from the older leaves, and I found after squirting on the leaves with water at 95 deg, all the older leaves became coated, after forty-eight hours, in an astonishing manner with a black Uredo, so that they looked as if sprinkled with soot and water. But not one of the younger leaves was affected. This has set me to work to see whether the "bloom" is not a protection against parasites. As soon as I have ascertained a little more about the case (and generally I am quite wrong at first) I will ask whether I could have a very small plant, which should never be syringed with water above 60 deg, and then I suspect the leaves would not be spotted, as were the older ones on the plant, when it arrived from Kew, but nothing like what they were after my squirting.
In an old note of yours (which I have just found) you say that you have a sensitive Schrankia: could this be lent me?
I have had lent me a young Coral-tree (Erythrina), which is very sickly, yet shows odd sleep movements. I suppose I could buy one, but Hooker told me first to ask you for anything.
Lastly, have you any seaside plants with bloom? I find that drops of sea-water corrode sea-kale if bloom is removed; also the var. littorum of Triticum repens. (By the way, my plants of the latter, grown in pots here, are now throwing up long flexible green blades, and it is very odd to see, ON THE SAME CULM, the rigid grey bloom-covered blades and the green flexible ones.) Cabbages, ill-luck to them, do not seem to be hurt by salt water. Hooker formerly told me that Salsola kali, a var. of Salicornia, one species of Suaeda, Euphorbia peplis, Lathyrus maritimus, Eryngium maritimum, were all glaucous and seaside plants. It is very improbable that you have any of these or of foreigners with the same attributes.
God forgive me: I hope that I have not bored you greatly.
By all the rules of right the leaves of the logwood ought to move (as if partially going to sleep) when syringed with tepid water. The leaves of my little plant do not move at all, and it occurs to me as possible, though very improbable, that it would be different with a larger plant with perhaps larger leaves. Would you some day get a gardener to syringe violently, with water kept in a hothouse, a branch on one of your largest logwood plants and observe {whether?} leaves move together towards the apex of leaf?
By the way, what astonishing nonsense Mr. Andrew Murray has been writing about leaves and carbonic acid! I like to see a man behaving consistently...
What a lot I have scribbled to you!
(FIGURE 13. Leaf of Trifolium resupinatum (from a drawing by Miss Pertz).)
LETTER 740. TO W. THISELTON-DYER. {August, 1877.}
There is no end to my requests. Can you spare me a good plant (or even two) of Oxalis sensitiva? The one which I have (formerly from Kew) has been so maltreated that I dare not trust my results any longer.
Please give the enclosed to Mr. Lynch. (740/1. Mr. Lynch, now Curator of the Cambridge Botanic Garden, was at this time in the R. Bot. Garden, Kew. Mr. Lynch described the movements of Averrhoa bilimbi in the "Linn. Soc. Journ," Volume XVI., page 231. See also "The Power of Movement in Plants," page 330.) The spontaneous movements of the Averrhoa are very curious.
You sent me seeds of Trifolium resupinatum, and I have raised plants, and some former observations which I did not dare to trust have proved accurate. It is a very little fact, but curious. The half of the lateral leaflets (marked by a cross) on the lower side have no bloom and are wetted, whereas the other half has bloom and is not wetted, so that the two sides look different to the naked eye. The cells of the eipdermis appear of a different shape and size on the two sides of the leaf {Figure 13}.
When we have drawings and measurements of cells made, and are sure of our facts, I shall ask you whether you know of any case of the same leaf differing histologically on the two sides, for Hooker always says you are a wonderful man for knowing what has been made out.
(740/2. The biological meaning of the curious structure of the leaves of Trifolium resupinatum remains a riddle. The stomata and (speaking from memory) the trichomes differ on the two halves of the lateral leaflets.)
LETTER 741. TO L. ERRERA.
(741/1. Professor L. Errera, of Brussels wrote, as a student, to Darwin, asking permission to send the MS. of an essay by his friend S. Gevaert and himself on cross and self-fertilisation, and which was afterwards published in the "Bull. Soc. Bot. Belg." XVII., 1878. The terms xenogamy, geitonogamy, and autogamy were first suggested by Kerner in 1876; their definition will be found at page 9 of Ogle's translation of Kerner's "Flowers and their Unbidden Guests," 1878. In xenogamy the pollen comes from another PLANT; in geitonogamy from another FLOWER on the same PLANT; in autogamy from the androecium of the fertilised FLOWER. Allogamy embraces xenogamy and geitonogamy.)
Down, October 4th, 1877.
I have now read your MS. The whole has interested me greatly, and is very clearly written. I wish that I had used some such terms as autogamy, xenogamy, etc...I entirely agree with you on the a priori probability of geitonogamy being more advantageous than autogamy; and I cannot remember having ever expressed a belief that autogamy, as a general rule, was better than geitonogamy; but the cases recorded by me seem too strong not to make me suspect that there was some unknown advantage in autogamy. In one place I insert the caution "if this be really the case," which you quote. (741/2. See "Cross and Self-Fertilisation," pages 352, 386. The phrase referred to occurs in both passages; that on page 386 is as follows: "We have also seen reason to suspect that self-fertilisation is in some peculiar manner beneficial to certain plants; but if this be really the case, the benefit thus derived is far more than counterbalanced by a cross with a fresh stock or with a slightly different variety." Errera and Gevaert conclude (pages 79-80) that the balance of the available evidence is in favour of the belief that geitonogamy is intermediate, in effectiveness, between autogamy and xenogamy.) I shall be very glad to be proved to be altogether in error on this point.
Accept my thanks for pointing out the bad erratum at page 301. I hope that you will experimentise on inconspicuous flowers (741/3. See Miss Bateson, "Annals of Botany," 1888, page 255, "On the Cross-Fertilisation of Inconspicuous Flowers:" Miss Bateson showed that Senecio vulgaris clearly profits by cross-fertilisation; Stellaria media and Capsella bursa-pastoris less certainly.); if I were not too old and too much occupied I would do so myself.
Finally let me thank you for the kind manner in which you refer to my work, and with cordial good wishes for your success...
LETTER 742. TO W. THISELTON-DYER. Down, October 9th, 1877.
One line to thank you much about Mertensia. The former plant has begun to make new leaves, to my great surprise, so that I shall be now well supplied. We have worked so well with the Averrhoa that unless the second species arrives in a very good state it would be superfluous to send it. I am heartily glad that you and Mrs. Dyer are going to have a holiday. I will look at you as a dead man for the next month, and nothing shall tempt me to trouble you. But before you enter your grave aid me if you can. I want seeds of three or four plants (not Leguminosae or Cruciferae) which produce large cotyledons. I know not in the least what plants have large cotyledons. Why I want to know is as follows: The cotyledons of Cassia go to sleep, and are sensitive to a touch; but what has surprised me much is that they are in constant movement up and down. So it is with the cotyledons of the cabbage, and therefore I am very curious to ascertain how far this is general.
LETTER 743. TO W. THISELTON-DYER. Down, October 11th {1877}.
The fine lot of seeds arrived yesterday, and are all sown, and will be most useful. If you remember, pray thank Mr. Lynch for his aid. I had not thought of beech or sycamore, but they are now sown.
Perhaps you may like to see a rough copy of the tracing of movements of one of the cotyledons of red cabbage, and you can throw it into the fire. A line joining the two cotyledons stood facing a north-east window, and the day was uniformly cloudy. A bristle was gummed to one cotyledon, and beyond it a triangular bit of card was fixed, and in front a vertical glass. A dot was made in the glass every quarter or half hour at the point where the end of the bristle and the apex of card coincided, and the dots were joined by straight lines. The observations were from 10 a.m. to 8.45 p.m. During this time the enclosed figure was described; but between 4 p.m. and 5.38 p.m. the cotyledon moved so that the prolonged line was beyond the limits of the glass, and the course is here shown by an imaginary dotted line. The cotyledon of Primula sinensis moved in closely analogous manner, as do those of a Cassia. Hence I expect to find such movements very general with cotyledons, and I am inclined to look at them as the foundation for all the other adaptive movements of leaves. They certainly are of the so-called sleep of plants.
I hope I have not bothered you. Do not answer. I am all on fire at the work.
I have had a short and very prosperous note from Asa Gray, who says Hooker is very prosperous, and both are tremendously hard at work. (743/1. "Hooker is coming over, and we are going in summer to the Rocky Mountains together, according to an old promise of mine." Asa Gray to G.F. Wright, May 24th, 1877 ("Letters of Asa Gray," II., page 666).)
LETTER 744. TO H. MULLER. Down, January 1st {1878?}.
I must write two or three lines to thank you cordially for your very handsome and very interesting review of my last book in "Kosmos," which I have this minute finished. (744/1. "Forms of Flowers," 1877. H. Muller's article is in "Kosmos," II., page 286.) It is wonderful how you have picked out everything important in it. I am especially glad that you have called attention to the parallelism between illegitimate offspring of heterostyled plants and hybrids. Your previous article in "Kosmos" seemed to me very important, but for some unknown reason the german was very difficult, and I was sadly overworked at the time, so that I could not understand a good deal of it. (744/2. "Kosmos," II., pages 11, 128. See "Forms of Flowers," Edition II., page 308.) But I have put it on one side, and when I have to prepare a new edition of my book I must make it out. It seems that you attribute such cases as that of the dioecious Rhamnus and your own of Valeriana to the existence of two forms with larger and smaller flowers. I cannot follow the steps by which such plants have been rendered dioecious, but when I read your article with more care I hope I shall understand. (744/3. See "Forms of Flowers," Edition II., pages 9 and 304. H. Muller's view is briefly that conspicuous and less conspicuous varieties occurred, and that the former were habitually visited first by insects; thus the less conspicuous form would play the part of females and their pollen would tend to become superfluous. See H. Muller in "Kosmos," II.) If you have succeeded in explaining this class of cases I shall heartily rejoice, for they utterly perplexed me, and I could not conjecture what their meaning was. It is a grievous evil to have no faculty for new languages.
With the most sincere respect and hearty good wishes to you and all your family for the new year...
P.S.—What interesting papers your wonderful brother has lately been writing!
LETTER 745. TO W. THISELTON-DYER.
(745/1. This letter refers to the purchase of instruments for the Jodrell Laboratory in the Royal Gardens, Kew. "The Royal Commission on Scientific Instruction and the Advancement of Science, commonly spoken of as the Devonshire Commission, in its fourth Report (1874), page 10, expressed the opinion that 'it is highly desirable that opportunities for the pursuit of investigations in Physiological Botany should be afforded at Kew to those persons who may be inclined to follow that branch of science.' Effect was given to this recommendation by the liberality of the late T.J. Phillips-Jodrell, M.A., who built and equipped the small laboratory, which has since borne his name, at his own expense. It was completed and immediately brought into use in 1876." The above is taken from the "Bulletin of Miscellaneous Information," R. Botanic Gardens, Kew, 1901, page 102, which also gives a list of work carried out in the laboratory between 1876 and 1900.)
Down, March 14th, 1878.
I have a very strong opinion that it would be the greatest possible pity if the Phys{iological} Lab., now that it has been built, were not supplied with as many good instruments as your funds can possibly afford. It is quite possible that some of them may become antiquated before they are much or even at all used. But this does not seem to me any argument at all against getting them, for the Laboratory cannot be used until well provided; and the mere fact of the instruments being ready may suggest to some one to use them. You at Kew, as guardians and promoters of botanical science, will then have done all in your power, and if your Lab. is not used the disgrace will lie at the feet of the public. But until bitter experience proves the contrary I will never believe that we are so backward. I should think the German laboratories would be very good guides as to what to get; but Timiriazeff of Moscow, who travelled over Europe to see all Bot. Labs., and who seemed so good a fellow, would, I should think, give the best list of the most indispensable instruments. Lately I thought of getting Frank or Horace to go to Cambridge for the use of the heliostat there; but our observations turned out of less importance than I thought, yet if there had been one at Kew we should probably have used it, and might have found out something curious. It is impossible for me to predict whether or not we should ever want this or that instrument, for we are guided in our work by what turns up. Thus I am now observing something about geotropism, and I had no idea a few weeks ago that this would have been necessary. In a short time we might earnestly wish for a centrifugal apparatus or a heliostat. In all such cases it would make a great difference if a man knew that he could use a particular instrument without great loss of time. I have now given my opinion, which is very decided, whether right or wrong, and Frank quite agrees with me. You can, of course, show this letter to Hooker.
LETTER 746. TO F. LUDWIG. Down, May 29th, 1878.
I thank you sincerely for the trouble which you have taken in sending me so long and interesting a letter, together with the specimens. Gradations are always very valuable, and you have been remarkably successful in discovering the stages by which the Plantago has become gyno-dioecious. (746/1. See F. Ludwig, "Zeitsch. f. d. Geo. Naturwiss." Bd. LII., 1879. Professor Ludwig's observations are quoted in the preface to "Forms of Flowers," Edition II., page ix.) Your view of its origin, from being proterogynous, seems to me very probable, especially as the females are generally the later-flowering plants. If you can prove the reverse case with Thymus your view will manifestly be rendered still more probable. I have never felt satisfied with H. Muller's view, though he is so careful and admirable an observer. (746/2. See "Forms of Flowers," Edition II., page 308. Also letter 744.) It is more than seventeen years since I attended to Plantago, and when nothing had been published on the subject, and in consequence I omitted to attend to several points; and now, after so long an interval, I cannot pretend to say to which of your forms the English one belongs; I well remember that the anther of the females contained a good deal {of} pollen, though not one sound grain.
P.S.—Delpino is Professor of Botany in Genoa, Italy (746/3. Now at Naples.); I have always found him a most obliging correspondent.
LETTER 747. TO W. THISELTON-DYER. Down, August 24th {1878}.
Many thanks for seeds of Trifolium resupinatum, which are invaluable to us. I enclose seeds of a Cassia, from Fritz Muller, and they are well worth your cultivation; for he says they come from a unique, large and beautiful tree in the interior, and though looking out for years, he has never seen another specimen. One of the most splendid, largest and rarest butterflies in S. Brazil, he has never seen except near this one tree, and he has just discovered that its caterpillars feed on its leaves.
I have just been looking at fine young pods beneath the ground of Arachis. (747/1. Arachis hypogoea, cultivated for its "ground nuts.") I suppose that the pods are not withdrawn when ripe from the ground; but should this be the case kindly inform me; if I do not hear I shall understand that {the} pods ripen and are left permanently beneath the ground.
If you ever come across heliotropic or apheliotropic aerial roots on a plant not valuable (but which should be returned), I should like to observe them. Bignonia capreolata, with its strongly apheliotropic tendrils (which I had from Kew), is now interesting me greatly. Veitch tells me it is not on sale in any London nursery, as I applied to him for some additional plants. So much for business.
I have received from the Geographical Soc. your lecture, and read it with great interest. (747/2. "On Plant-Distribution as a field for Geographical Research." "Geog. Soc. Proc." XXII., 1878, page 412.) But it ought not merely to be read; it requires study. The sole criticism which I have to make is that parts are too much condensed: but, good Lord, how rare a fault is this! You do not quote Saporta, I think; and some of his work on the Tertiary plants would have been useful to you. In a former note you spoke contemptuously of your lecture: all I can say is that I never heard any one speak more unjustly and shamefully of another than you have done of yourself!
LETTER 748. TO H. MULLER. Down, September 20th, 1878.
I am working away on some points in vegetable physiology, but though they interest me and my son, yet they have none of the fascination which the fertilisation of flowers possesses. Nothing in my life has ever interested me more than the fertilisation of such plants as Primula and Lythrum, or again Anacamptis (748/1. Orchis pyramidalis.) or Listera.
LETTER 749. TO H. MULLER. Down, February 12th {1879}.
I have just heard that some misfortune has befallen you, and that you have been treated shamefully. (749/1. Hermann Muller was accused by the Ultramontane party of introducing into his school-teaching crude hypotheses ("unreife Hypothesen"), which were assumed to have a harmful influence upon the religious sentiments of his pupils. Attempts were made to bring about Muller's dismissal, but the active hostility of his opponents, which he met in a dignified spirit, proved futile. ("Prof. Dr. Hermann Muller von Lippstadt. Ein Gedenkblatt," von Ernst Krause. "Kosmos," VII., page 393, 1883.)) I grieve deeply to hear this, and as soon as you can find a few minutes to spare, I earnestly beg you to let me hear what has happened.
LETTER 750. TO A. STEPHEN WILSON.
(750/1. The following letters refer to two forms of wheat cultivated in Russia under the names Kubanka and Saxonka, which had been sent to Mr. Darwin by Dr. Asher from Samara, and were placed in the hands of Mr. Wilson that he might test the belief prevalent in Russia that Kubanka "grown repeatedly on inferior soil," assumes "the form of Saxonka." Mr. Wilson's paper of 1880 gives the results of his inquiry. He concludes (basing his views partly on analogous cases and partly on his study of the Russian wheats) that the supposed transformation is explicable in chief part by the greater fertility of the Saxonka wheat leading to extermination of the other form. According to Mr. Wilson, therefore, the Saxonka survivors are incorrectly assumed to be the result of the conversion of one form into the other.)
Down, April 24th, 1878.
I send you herewith some specimens which may perhaps interest you, as you have so carefully studied the varieties of wheat. Anyhow, they are of no use to me, as I have neither knowledge nor time sufficient. They were sent me by the Governor of the Province of Samara, in Russia, at the request of Dr. Asher (son of the great Berlin publisher) who farmed for some years in the province. The specimen marked Kubanka is a very valuable kind, but which keeps true only when cultivated in fresh steppe-land in Samara, and in Saratoff. After two years it degenerates into the variety Saxonica, or its synonym Ghirca. The latter alone is imported into this country. Dr. Asher says that it is universally known, and he has himself witnessed the fact, that if grain of the Kubanka is sown in the same steppe-land for more than two years it changes into Saxonica. He has seen a field with parts still Kubanka and the remainder Saxonica. On this account the Government, in letting steppe-land, contracts that after two years wheat must not be sown until an interval of eight years. The ears of the two kinds appear different, as you will see, but the chief difference is in the quality of the grains. Dr. Asher has witnessed sales of equal weights of Kubanka and Saxonica grain, and the price of the former was to that of the latter as 7 to 4. The peasants say that the change commences in the terminal grain of the ear. The most remarkable point, as Dr. Asher positively asserts, is that there are no intermediate varieties; but that a grain produces a plant yielding either true Kubanka or true Saxonica. He thinks that it would be interesting to sow here both kinds in good and bad wheat soil and observe the result. Should you think it worth while to make any such trial, and should you require further information, Dr. Asher, whose address I enclose, will be happy to give any in his power.
LETTER 751. TO A. STEPHEN WILSON. Basset, Southampton, April 29th {1878}.
Your kind note and specimens have been forwarded to me here, where I am staying at my son's house for a fortnight's complete rest, which I required from rather too hard work. For this reason I will not now examine the seeds, but will wait till returning home, when, with my son Francis' aid, I will look to them.
I always felt, though without any good reason, rather sceptical about Prof. Buckman's experiment, and I afterwards heard that a most wicked and cruel trick had been played on him by some of the agricultural students at Cirencester, who had sown seeds unknown to him in his experimental beds. Whether he ever knew this I did not hear.
I am exceedingly glad that you are willing to look into the Russian wheat case. It may turn out a mare's nest, but I have often incidentally observed curious facts when making what I call "a fool's experiment."
LETTER 752. TO A. STEPHEN WILSON. Down, March 5th, 1879.
I have just returned home after an absence of a week, and your letter was not forwarded to me; I mention this to account for my apparent discourtesy in not having sooner thanked you. You have worked out the subject with admirable care and clearness, and your drawings are beautiful. I suspected that there was some error in the Russian belief, but I did not think of the explanation which you have almost proved to be the true one. It is an extremely interesting instance of a more fertile variety beating out a less fertile one, and, in this case, one much more valuable to man. With respect to publication, I am at a loss to advise you, for I live a secluded life and do not see many periodicals, or hear what is done at the various societies. It seems to me that your paper should be published in some agricultural journal; for it is not simply scientific, and would therefore not be published by the Linnean or Royal Societies.
Would the Royal Agricultural Society be a fitting place? Unfortunately I am not a member, and could not myself present it. Unless you think of some better journal, there is the "Agricultural Gazette": I have occasionally suggested articles for publication to the editor (though personally unknown to me) which he has always accepted.
Permit me again to thank you for the thorough manner in which you have worked out this case; to kill an error is as good a service as, and sometimes even better than, the establishing a new truth or fact.
LETTER 753. TO A. STEPHEN WILSON. Down, February 13th, 1880.
It was very kind of you to send me two numbers of the "Gardeners' Chronicle" with your two articles, which I have read with much interest. (753/1. "Gardeners' Chronicle," 1879, page 652; 1880, pages 108, 173.) You have quite convinced me, whatever Mr. Asher may say to the contrary. I want to ask you a question, on the bare chance of your being able to answer it, but if you cannot, please do not take the trouble to write. The lateral branches of the silver fir often grow out into knobs through the action of a fungus, Aecidium; and from these knobs shoots grow vertically (753/2. The well-known "Witches-Brooms," or "Hexen-Besen," produced by the fungus Aecidium elatinum.) instead of horizontally, like all the other twigs on the same branch. Now the roots of Cruciferae and probably other plants are said to become knobbed through the action of a fungus: now, do these knobs give rise to rootlets? and, if so, do they grow in a new or abnormal direction? (753/3. The parasite is probably Plasmodiophora: in this case no abnormal rootlets have been observed, as far as we know.)
LETTER 754. TO W. THISELTON-DYER. Down, June 18th, 1879.
The plants arrived last night in first-rate order, and it was very very good of you to take so much trouble as to hunt them up yourself. They seem exactly what I wanted, and if I fail it will not be for want of perfect materials. But a confounded painter (I beg his pardon) comes here to-night, and for the next two days I shall be half dead with sitting to him; but after then I will begin to work at the plants and see what I can do, and very curious I am about the results.
I have to thank you for two very interesting letters. I am delighted to hear, and with surprise, that you care about old Erasmus D. God only knows what I shall make of his life—it is such new kind of work to me. (754/1. "Erasmus Darwin." By Ernst Krause. Translated from the German by W.S. Dallas: with a preliminary notice by Charles Darwin. London, 1879. See "Life and Letters," III., pages 218-20.)
Thanks for case of sleeping Crotalaria—new to me. I quite agree to every word you say about Ball's lecture (754/2. "On the Origin of the Flora of the European Alps," "Geogr. Soc. Proc." Volume I., 1879, page 564. See Letter 395, Volume II.)—it is, as you say, like Sir W. Thomson's meteorite. (754/3. In 1871 Lord Kelvin (Presidential Address Brit. Assoc.) suggested that meteorites, "the moss-grown fragments from the ruins of another world," might have introduced life to our planet.) It is really a pity; it is enough to make Geographical Distribution ridiculous in the eyes of the world. Frank will be interested about the Auriculas; I never attended to this plant, for the powder did {not} seem to me like true "bloom." (754/4. See Francis Darwin, on the relation between "bloom" on leaves and the distribution of the stomata. "Linn. Soc. Journ." Volume XXII., page 114.) This subject, however, for the present only, has gone to the dogs with me.
I am sorry to hear of such a struggle for existence at Kew; but I have often wondered how it is that you are all not killed outright.
I can most fully sympathise with you in your admiration of your little girl. There is nothing so charming in this world, and we all in this house humbly adore our grandchild, and think his little pimple of a nose quite beautiful.
LETTER 755. TO G. BENTHAM. Down, February 16th, 1880.
I have had real pleasure in signing Dyer's certificate. (755/1. As a candidate for the Royal Society.) It was very kind in you to write to me about the Orchideae, for it has pleased me to an extreme degree that I could have been of the least use to you about the nature of the parts. They are wonderful creatures, these orchids, and I sometimes think with a glow of pleasure, when I remember making out some little point in their method of fertilisation. (755/2. Published in "Life and Letters," III., page 288.) With respect to terms, no doubt you will be able to improve them greatly, for I knew nothing about the terms as used in other groups of plants. Could you not invent some quite new term for gland, implying viscidity? or append some word to gland. I used for cirripedes "cement gland."
Your present work must be frightfully difficult. I looked at a few dried flowers, and could make neither heads nor tails of them; and I well remember wondering what you would do with them when you came to the group in the "Genera Plantarum." I heartily wish you safe through your work,...
LETTER 756. TO F.M. BALFOUR. Down, September 4th, 1880.
I hope that you will not think me a great bore, but I have this minute finished reading your address at the British Association; and it has interested me so much that I cannot resist thanking you heartily for the pleasure derived from it, not to mention the honour which you have done me. (756/1. Presidential address delivered by Prof. F.M. Balfour before the Biological Section at the British Association meeting at Swansea (1880).) The recent progress of embryology is indeed splendid. I have been very stupid not to have hitherto read your book, but I have had of late no spare time; I have now ordered it, and your address will make it the more interesting to read, though I fear that my want of knowledge will make parts unintelligible to me. (756/2. "A Treatise on Comparative Embryology," 2 volumes. London, 1880.) In my recent work on plants I have been astonished to find to how many very different stimuli the same small part—viz., the tip of the radicle—is sensitive, and has the power of transmitting some influence to the adjoining part of the radicle, exciting it to bend to or from the source of irritation according to the needs of the plant (756/3. See Letter 757.); and all this takes place without any nervous system! I think that such facts should be kept in mind when speculating on the genesis of the nervous system. I always feel a malicious pleasure when a priori conclusions are knocked on the head: and therefore I felt somewhat like a devil when I read your remarks on Herbert Spencer (756/4. Prof. Balfour discussed Mr. Herbert Spencer's views on the genesis of the nervous system, and expressed the opinion that his hypothesis was not borne out by recent discoveries. "The discovery that nerves have been developed from processes of epithelial cells gives a very different conception of their genesis to that of Herbert Spencer, which makes them originate from the passage of nervous impulses through a track of mingled colloids..." (loc. cit., page 644.))...Our recent visit to Cambridge was a brilliant success to us all, and will ever be remembered by me with much pleasure.
LETTER 757. TO JAMES PAGET.
(757/1. During the closing years of his life, Darwin began to experimentise on the possibility of producing galls artificially. A letter to Sir J.D. Hooker (November 3rd, 1880) shows the interest which he felt in the question:—
"I was delighted with Paget's essay (757/2. An address on "Elemental Pathology," delivered before the British Medical Association, August 1880, and published in the Journal of the Association.); I hear that he has occasionally attended to this subject from his youth...I am very glad he has called attention to galls: this has always seemed to me a profoundly interesting subject; and if I had been younger would take it up."
His interest in this subject was connected with his ever-present wish to learn something of the causes of variation. He imagined to himself wonderful galls caused to appear on the ovaries of plants, and by these means he thought it possible that the seed might be influenced, and thus new varieties arise. (757/3. There would have been great difficulties about this line of research, for when the sexual organs of plants are deformed by parasites (in the way he hoped to effect by poisons) sterility almost always results. See Molliard's "Les Cecidies Florales," "Ann. Sci. Nat." 1895, Volume I., page 228.) He made a considerable number of experiments by injecting various reagents into the tissues of leaves, and with some slight indications of success. (757/4. The above passage is reprinted, with alterations, from "Life and Letters," III., page 346.)
The following letter to the late Sir James Paget refers to the same subject.)
Down, November 14th, 1880.
I am very much obliged for your essay, which has interested me greatly. What indomitable activity you have! It is a surprising thought that the diseases of plants should illustrate human pathology. I have the German "Encyclopaedia," and a few weeks ago told my son Francis that the article on the diseases of plants would be well worth his study; but I did not know it was written by Dr. Frank, for whom I entertain a high respect as a first-rate observer and experimentiser, though for some unknown reason he has been a good deal snubbed in Germany. I can give you one good case of regrowth in plants, recently often observed by me, though only externally, as I do not know enough of histology to follow out details. It is the tip of the radicle of a germinating common bean. The case is remarkable in some respects, for the tip is sensitive to various stimuli, and transmits an order, causing the upper part of the radicle to bend. When the tip (for a length of about 1 mm.) is cut transversely off, the radicle is not acted on by gravitation or other irritants, such as contact, etc., etc., but a new tip is regenerated in from two to four days, and then the radicle is again acted on by gravitation, and will bend to the centre of the earth. The tip of the radicle is a kind of brain to the whole growing part of the radicle! (757/5. We are indebted to Mr. Archer-Hind for the translation of the following passage from Plato ("Timaeus," 90A): "The reason is every man's guardian genius (daimon), and has its habitation in our brain; it is this that raises man (who is a plant, not of earth but of heaven) to an erect posture, suspending the head and root of us from the heavens, which are the birthplace of our soul, and keeping all the body upright." On the perceptions of plants, see "Nature," November 14th, 1901—a lecture delivered at the Glasgow meeting of the British Association by Francis Darwin. See also Bonitz, "Index Aristotelicus," S.V. phuton.)
My observation will be published in about a week's time, and I would have sent you the book, but I do not suppose that there is anything else in the book which would interest you. I am delighted that you have drawn attention to galls. They have always seemed to me profoundly interesting. Many years ago I began (but failed for want of time, strength, and health, as on infinitely many other occasions) to experimentise on plants, by injecting into their tissues some alkaloids and the poison of wasps, to see if I could make anything like galls. If I remember rightly, in a few cases the tissues were thickened and hardened. I began these experiments because if by different poisons I could have affected slightly and differently the tissues of the same plant, I thought there would be no insuperable difficulty in the fittest poisons being developed by insects so as to produce galls adapted for them. Every character, as far as I can see, is apt to vary. Judging from one of your sentences you will smile at this.
To any one believing in my pangenesis (if such a man exists) there does not seem to me any extreme difficulty in understanding why plants have such little power of regeneration; for there is reason to think that my imaginary gemmules have small power of passing from cell to cell. (757/6. On regeneration after injury, see Massart, "La Cicatrisation chez les Vegetaux," in Volume 57 (1898) of the "Memoires Couronnes," published by the Royal Academy of Belgium. An account of the literature is given by the author.)
Forgive me for scribbling at such unreasonable length; but you are to blame for having interested me so much.
P.S.—Perhaps you may remember that some two years ago you asked me to lunch with you, and proposed that I should offer myself again. Whenever I next come to London, I will do so, and thus have the pleasure of seeing you.
LETTER 758. TO W. THISELTON-DYER.
(758/1. "The Power of Movement in Plants" was published early in November, 1880. Sir W. Thiselton-Dyer, in writing to thank Darwin for a copy of the book, had (November 20th) compared a structure in the seedling Welwitschia with the "peg" of Cucurbita (see "Power of Movement," page 102). Dyer wrote: "One peculiar feature in the germinating embryo is a lateral hypocotyledonary process, which eventually serves as an absorbent organ, by which the nutriment of the endosperm is conveyed to the seedling. Such a structure was quite new to me, and Bower and I were disposed to see in it a representative of the foot in Selaginella, when I saw the account of Flahault's 'peg.'" Flahault, it should be explained, was the discoverer of the curious peg in Cucurbita. Prof. Bower wrote a paper ("On the Germination and Histology of the seedling of Welwitschia mirabilis" in the "Quart. Journ. Microscop. Sci." XXI., 1881, page 15.)
Down, November 28th {1880}.
Very many thanks for your most kind note, but you think too highly of our work—not but what this is very pleasant.
I am deeply interested about Welwitschia. When at work on the pegs or projections I could not imagine how they were first developed, before they could have been of mere mechanical use. Now it seems possible that a circle between radicle and hypocotyl may be permeable to fluids, and thus have given rise to projections so as to expose larger surface. Could you test Welwitschia with permanganate of potassium: if, like my pegs, the lower surface would be coloured brown like radicle, and upper surface left white like hypocotyl. If such an idea as yours, of an absorbing organ, had ever crossed my mind, I would have tried many hypocotyls in weak citrate of ammonia, to see if it penetrated on line of junction more easily than elsewhere. I daresay the projection in Abronia and Mirabilis may be an absorbent organ. It was very good fun bothering the seeds of Cucurbita by planting them edgeways, as would never naturally occur, and then the peg could not act properly. Many of the Germans are very contemptuous about making out use of organs; but they may sneer the souls out of their bodies, and I for one shall think it the most interesting part of natural history. Indeed, you are greatly mistaken if you doubt for one moment on the very great value of your constant and most kind assistance to us. I have not seen the pamphlet, and shall be very glad to keep it. Frank, when he comes home, will be much interested and pleased with your letter. Pray give my kindest remembrance to Mrs. Dyer.
This is a very untidy note, but I am very tired with dissecting worms all day. Read the last chapter of our book, and then you will know the whole contents.
LETTER 759. TO H. VOCHTING. Down, December 16th, 1880.
Absence from home has prevented me from sooner thanking you for your kind present of your several publications. I procured some time ago your "Organbilding" (759/1. "Organbildung im Pflanzenreich," 1878.) etc., but it was too late for me to profit by it for my book, as I was correcting the press. I read only parts, but my son Francis read the whole with care and told me much about it, which greatly interested me. I also read your article in the "Bot. Zeitung." My son began at once experimenting, to test your views, and this very night will read a paper before the Linnean Society on the roots of Rubus (759/2. Francis Darwin, "The Theory of the Growth of Cuttings" ("Linn. Soc. Journ." XVIII.). {I take this opportunity of expressing my regret that at page 417, owing to neglect of part of Vochting's facts, I made a criticism of his argument which cannot be upheld.—F.D.}.), and I think that you will be pleased to find how well his conclusions agree with yours. He will of course send you a copy of his paper when it is printed. I have sent him your letter, which will please him if he agrees with me; for your letter has given me real pleasure, and I did not at all know what the many great physiologists of Germany, Switzerland, and Holland would think of it {"The Power of Movement," etc.}. I was quite sorry to read Sachs' views about root-forming matter, etc., for I have an unbounded admiration for Sachs. In this country we are dreadfully behind in Physiological Botany.
LETTER 760. TO A. DE CANDOLLE. Down, January 24th, 1881.
It was extremely kind of you to write me so long and valuable a letter, the whole of which deserves careful consideration. I have been particularly pleased at what you say about the new terms used, because I have often been annoyed at the multitude of new terms lately invented in all branches of Biology in Germany; and I doubted much whether I was not quite as great a sinner as those whom I have blamed. When I read your remarks on the word "purpose" in your "Phytographie," I vowed that I would not use it again; but it is not easy to cure oneself of a vicious habit. It is also difficult for any one who tries to make out the use of a structure to avoid the word purpose. I see that I have probably gone beyond my depth in discussing plurifoliate and unifoliate leaves; but in such a case as that of Mimosa albida, where rudiments of additional leaflets are present, we must believe that they were well developed in the progenitor of the plant. So again, when the first true leaf differs widely in shape from the older leaves, and resembles the older leaves in allied species, is it not the most simple explanation that such leaves have retained their ancient character, as in the case of the embryos of so many animals?
Your suggestion of examining the movements of vertical leaves with an equal number of stomata on both sides, with reference to the light, seems to me an excellent one, and I hope that my son Francis may follow it up. But I will not trouble you with any more remarks about our book. My son will write to you about the diagram.
Let me add that I shall ever remember with pleasure your visit here last autumn.
LETTER 761. TO J. LUBBOCK (Lord Avebury). Down, April 16th {1881}.
Will you be so kind as to send and lend me the Desmodium gyrans by the bearer who brings this note.
Shortly after you left I found my notice of the seeds in the "Gardeners' Chronicle," which please return hereafter, as I have no other copy. (761/1. "Note on the Achenia of Pumilio argyrolepis." "Gardeners' Chronicle," 1861, page 4.) I do not think that I made enough about the great power of absorption of water by the corolla-like calyx or pappus. It seems to me not unlikely that the pappus of other Compositae may be serviceable to the seeds, whilst lying on the ground, by absorbing the dew which would be especially apt to condense on the fine points and filaments of the pappus. Anyhow, this is a point which might be easily investigated. Seeds of Tussilago, or groundsel (761/2. It is not clear whether Tussilago or groundsel (Senecio vulgaris) is meant; or whether he was not sure which of the two plants becomes slimy when wetted.), emit worm-like masses of mucus, and it would be curious to ascertain whether wetting the pappus alone would suffice to cause such secretion. (761/3. See Letter 707.)
LETTER 762. TO G.J. ROMANES. Down, April 18th, 1881.
I am extremely glad of your success with the flashing light. (762/1. Romanes' paper on the effect of intermittent light on heliotropism was the "Proc. Royal Soc." Volume LIV., page 333.) If plants are acted on by light, like some of the lower animals, there is an additional point of interest, as it seems to me, in your results. Most botanists believe that light causes a plant to bend to it in as direct a manner as light affects nitrate of silver. I believe that it merely tells the plant to which side to bend, and I see indications of this belief prevailing even with Sachs. Now it might be expected that light would act on a plant in something the same manner as on the lower animals. As you are at work on this subject, I will call your attention to another point. Wiesner, of Vienna (who has lately published a great book on heliotropism) finds that an intermittent light, say of 20 minutes, produces the same effect as a continuous light of, say 60 m. (762/2. Wiesner's papers on heliotropism are in the "Denkschriften" of the Vienna Academy, Volumes 39 and 43.) So that Van Tieghem, in the first part of his book which has just appeared, remarks, the light during 40 m. out of the 60 m. produced no effect. I observed an analogous case described in my book. (762/3. "Power of Movement," page 459.)
Wiesner and Van Tieghem seem to think that this is explained by calling the whole process "induction," borrowing a term used by some physico-chemists (of whom I believe Roscoe is one) and implying an agency which does not produce any effect for some time, and continues its effect for some time after the cause has ceased. I believe that photographic paper is an instance. I must ask Leonard (762/4. Mr. Darwin's son.) whether an interrupted light acts on it in the same manner as on a plant. At present I must still believe in my explanation that it is the contrast between light and darkness which excites a plant.
I have forgotten my main object in writing—viz., to say that I believe (and have so stated) that seedlings vary much in their sensitiveness to light; but I did not prove this, for there are many difficulties, whether the time of incipient curvature or the amount of curvature is taken as the criterion. Moreover they vary according to age, and perhaps from vigour of growth, and there seems inherent variability, as Strasburger (whom I quote) found with spores. If the curious anomaly observed by you is due to varying sensitiveness, ought not all the seedlings to bend if the flashes were at longer intervals of time? According to my notion of contrast between light and darkness being the stimulus, I should expect that if flashes were made sufficiently slow it would be a powerful stimulus, and that you would suddenly arrive at a period when the result would SUDDENLY become great. On the other hand, as far as my experience goes, what one expects rarely happens.
LETTER 763. TO JULIUS WIESNER. Down, October 4th, 1881.
I thank you sincerely for your very kind letter, and for the present of your new work. (763/1. "Das Bewegungsvermogen der Pflanze," 1881. One of us has given some account of Wiesner's book in the presidential address to Section D of the British Association, 1891. Wiesner's divergence from Darwin's views is far-reaching, and includes the main thesis of the "Power of Movement." See "Life and Letters," III., page 336, for an interesting letter to Wiesner.) My son Francis, if he had been at home, would have likewise sent his thanks. I will immediately begin to read your book, and when I have finished it will write again. But I read german so very slowly that your book will take me a considerable time, for I cannot read for more than half an hour each day. I have, also, been working too hard lately, and with very little success, so that I am going to leave home for a time and try to forget science.
I quite expect that you will find some gross errors in my work, for you are a very much more skilful and profound experimentalist than I am. Although I always am endeavouring to be cautious and to mistrust myself, yet I know well how apt I am to make blunders. Physiology, both animal and vegetable, is so difficult a subject, that it seems to me to progress chiefly by the elimination or correction of ever-recurring mistakes. I hope that you will not have upset my fundamental notion that various classes of movement result from the modification of a universally present movement of circumnutation.
I am very glad that you will again discuss the view of the turgescence of the cells being the cause of the movement of parts. I adopted De Vries' views as seeming to me the most probable, but of late I have felt more doubts on this head. (763/2. See "Power of Movement," page 2. De Vries' work is published in the "Bot. Zeitung," 1879, page 830.)
LETTER 764. TO J.D. HOOKER. Glenrhydding House, Patterdale, Penrith, June 15th, 1881.
It was real pleasure to me to see once again your well-known handwriting on the outside of your note. I do not know how long you have returned from Italy, but I am very sorry that you are so bothered already with work and visits. I cannot but think that you are too kind and civil to visitors, and too conscientious about your official work. But a man cannot cure his virtues, any more than his vices, after early youth; so you must bear your burthen. It is, however, a great misfortune for science that you have so very little spare time for the "Genera." I can well believe what an awful job the palms must be. Even their size must be very inconvenient. You and Bentham must hate the monocotyledons, for what work the Orchideae must have been, and Gramineae and Cyperaceae will be. I am rather despondent about myself, and my troubles are of an exactly opposite nature to yours, for idleness is downright misery to me, as I find here, as I cannot forget my discomfort for an hour. I have not the heart or strength at my age to begin any investigation lasting years, which is the only thing which I enjoy; and I have no little jobs which I can do. So I must look forward to Down graveyard as the sweetest place on earth. This place is magnificently beautiful, and I enjoy the scenery, though weary of it; and the weather has been very cold and almost always hazy.
I am so glad that your tour has answered for Lady Hooker. We return home on the first week of July, and should be truly glad to aid Lady Hooker in any possible manner which she will suggest.
I have written to my gardener to send you plants of Oxalis corniculata (and seeds if possible). I should think so common a weed was never asked for before,—and what a poor return for the hundreds of plants which I have received from Kew! I hope that I have not bothered you by writing so long a note, and I did not intend to do so.
If Asa Gray has returned with you, please give him my kindest remembrances.
LETTER 765. TO J.D. HOOKER. October 22nd, 1881.
I am investigating the action of carbonate of ammonia on chlorophyll, which makes me want the plants in my list. (765/1. "The Action of Carbonate of Ammonia on Chlorophyll Bodies." "Linn. Soc. Journ." XIX., page 262, 1882.) I have incidentally observed one point in Euphorbia, which has astonished me—viz. that in the fine fibrous roots of Euphorbia, the alternate rows of cells in their roots must differ physiologically, though not in external appearance, as their contents after the action of carbonate of ammonia differ most conspicuously...
Wiesner of Vienna has just published a book vivisecting me in the most courteous, but awful manner, about the "Power of Movement in Plants." (765/2. See Letter 763, note.) Thank heaven, he admits almost all my facts, after re-trying all my experiments; but gives widely different interpretation of the facts. I think he proves me wrong in several cases, but I am convinced that he is utterly erroneous and fanciful in other explanations. No man was ever vivisected in so sweet a manner before, as I am in this book.
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