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 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 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 in the desolating flood from which you suffered. Forgive me, but why should you not order, through your brother Hermann, , 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 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 (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 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 (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 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 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 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 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 (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 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 "Harvesting Ants and Trap-Door Spiders," 1873, which is full of interesting details. The 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 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 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 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 "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 brbrimmed 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 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 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.)
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