Чарльз Дарвин
Life and Letters of Charles Darwin — Volume 2
Your suggestion of studying the manner of fertilisation of the surviving members of the most ancient forms of the dicotyledons is a very good one, and I hope that you will keep it in mind yourself, for I have turned my attention to other subjects. Delpino I think says that Magnolia is fertilised by insects which gnaw the petals, and I should not be surprised if the same fact holds good with Nymphaea. Whenever I have looked at the flowers of these latter plants I have felt inclined to admit the view that petals are modified stamens, and not modified leaves; though Poinsettia seems to show that true leaves might be converted into coloured petals. I grieve to say that I have never been properly grounded in Botany and have studied only special points — therefore I cannot pretend to express any opinion on your remarks on the origin of the flowers of the Coniferae, Gnetaceae, etc.; but I have been delighted with what you say on the conversion of a monoecious species into a hermaphrodite one by the condensations of the verticils on a branch bearing female flowers near the summit, and male flowers below.
I expect Hooker to come here before long, and I will then show him your drawing, and if he makes any important remarks I will communicate with you. He is very busy at present in clearing off arrears after his American Expedition, so that I do not like to trouble him, even with the briefest note. I am at present working with my son at some Physiological subjects, and we are arriving at very curious results, but they are not as yet sufficiently certain to be worth communicating to you...
[In 1877 a second edition of the 'Fertilisation of Orchids' was published, the first edition having been for some time out of print. The new edition was remodelled and almost re-written, and a large amount of new matter added, much of which the author owed to his friend Fritz Muller.
With regard to this edition he wrote to Dr. Gray: —
"I do not suppose I shall ever again touch the book. After much doubt I have resolved to act in this way with all my books for the future; that is to correct them once and never touch them again, so as to use the small quantity of work left in me for new matter."
He may have felt a diminution of his powers of reviewing large bodies of facts, such as would be needed in the preparation of new editions, but his powers of observation were certainly not diminished. He wrote to Mr. Dyer on July 14, 1878:]
My dear Dyer,
Thalia dealbata was sent me from Kew: it has flowered and after looking casually at the flowers, they have driven me almost mad, and I have worked at them for a week: it is as grand a case as that of Catasetum.
Pistil vigorously motile (so that whole flower shakes when pistil suddenly coils up); when excited by a touch the two filaments [are] produced laterally and transversely across the flower (just over the nectar) from one of the petals or modified stamens. It is splendid to watch the phenomenon under a weak power when a bristle is inserted into a YOUNG flower which no insect has visited. As far as I know Stylidium is the sole case of sensitive pistil and here it is the pistil + stamens. In Thalia (Hildebrand has described an explosive arrangement in some of the Maranteae — the tribe to which Thalia belongs.) cross-fertilisation is ensured by the wonderful movement, if bees visit several flowers.
I have now relieved my mind and will tell the purport of this note — viz. if any other species of Thalia besides T. dealbata should flower with you, for the love of heaven and all the saints, send me a few in TIN BOX WITH DAMP MOSS.
Your insane friend, CH. DARWIN.
[In 1878 Dr. Ogle's translation of Kerner's interesting book, 'Flowers and their Unbidden Guests,' was published. My father, who felt much interest in the translation (as appears in the following letter), contributed some prefatory words of approval:]
CHARLES DARWIN TO W. OGLE. Down, December 16 [1878].
... I have now read Kerner's book, which is better even than I anticipated. The translation seems to me as clear as daylight, and written in forcible and good familiar English. I am rather afraid that it is too good for the English public, which seems to like very washy food, unless it be administered by some one whose name is well-known, and then I suspect a good deal of the unintelligible is very pleasing to them. I hope to heaven that I may be wrong. Anyhow, you and Mrs. Ogle have done a right good service for Botanical Science. Yours very sincerely,
CH. DARWIN.
P.S. — You have done me much honour in your prefatory remarks.
[One of the latest references to his Orchid-work occurs in a letter to Mr. Bentham, February 16, 1880. It shows the amount of pleasure which this subject gave to my father, and (what is characteristic of him) that his reminiscence of the work was one of delight in the observations which preceded its publication. Not to the applause which followed it: —
"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."]
CHAPTER 2.XI. — THE 'EFFECTS OF CROSS- AND SELF-FERTILISATION
IN THE VEGETABLE KINGDOM.'
1876.
[This book, as pointed out in the 'Autobiography,' is a complement to the 'Fertilisation of Orchids,' because it shows how important are the results of cross-fertilisation which are ensured by the mechanisms described in that book.
By proving that the offspring of cross-fertilisation are more vigorous than the offspring of self-fertilisation, he showed that one circumstance which influences the fate of young plants in the struggle for life is the degree to which their parents are fitted for cross-fertilisation. He thus convinced himself that the intensity of the struggle (which he had elsewhere shown to exist among young plants) is a measure of the strength of a selective agency perpetually sifting out every modification in the structure of flowers which can effect its capabilities for cros-fertilisation.
The book is also valuable in another respect, because it throws light on the difficult problems of the origin of sexuality. The increased vigour resulting from cross-fertilisation is allied in the closest manner to the advantage gained by change of conditions. So strongly is this the case, that in some instances cross-fertilisation gives no advantage to the offspring, unless the parents have lived under slightly different conditions. So that the really important thing is not that two individuals of different BLOOD shall unite, but two individuals which have been subjected to different conditions. We are thus led to believe that sexuality is a means for infusing vigour into the offspring by the coalescence of differentiated elements, an advantage which could not follow if reproductions were entirely asexual.
It is remarkable that this book, the result of eleven years of experimental work, owed its origin to a chance observation. My father had raised two beds of Linaria vulgaris — one set being the offspring of cross- and the other of self-fertilisation. These plants were grown for the sake of some observations on inheritance, and not with any view to cross-breeding, and he was astonished to observe that the offspring of self-fertilisation were clearly less vigorous than the others. It seemed incredible to him that this result could be due to a single act of self-fertilisation, and it was only in the following year when precisely the same result occurred in the case of a similar experiment on inheritance in Carnations, that his attention was "thoroughly aroused" and that he determined to make a series of experiments specially directed to the question. The following letters give some account of the work in question.]
CHARLES DARWIN TO ASA GRAY. September 10, [1866?].
... I have just begun a large course of experiments on the germination of the seed, and on the growth of the young plants when raised from a pistil fertilised by pollen from the same flower, and from pollen from a distinct plant of the same, or of some other variety. I have not made sufficient experiments to judge certainly, but in some cases the difference in the growth of the young plants is highly remarkable. I have taken every kind of precaution in getting seed from the same plant, in germinating the seed on my own chimney-piece, in planting the seedlings in the same flower-pot, and under this similar treatment I have seen the young seedlings from the crossed seed exactly twice as tall as the seedlings from the sel-fertilised seed; both seeds having germinated on the same day. If I can establish this fact (but perhaps it will all go to the dogs), in some fifty cases, with plants of different orders, I think it will be very important, for then we shall positively know why the structure of every flower permits, or favours, or necessitates an occasional cross with a distinct individual. But all this is rather cooking my hare before I have caught it. But somehow it is a great pleasure to me to tell you what I am about. Believe me, my dear Gray,
Ever yours most truly, and with cordial thanks, CH. DARWIN.
CHARLES DARWIN TO G. BENTHAM. April 22, 1868.
... I am experimenting on a very large scale on the difference in power of 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.
With cordial thanks for your letter, which has pleased me greatly,
Yours very sincerely, CHARLES DARWIN.
[An extract from a letter to Dr. Gray (March 11, 1873) mentions the progress of the work: —
"I worked last summer hard at Drosera, but could not finish till I got fresh plants, and consequently took up the effects of crossing and sel-fertilising plants, and am got so interested that Drosera must go to the dogs till I finish with this, and get it published; but then I will resume my beloved Drosera, and I heartily apologise for having sent the precious little things even for a moment to the dogs."
The following letters give the author's impression of his own book.]
CHARLES DARWIN TO J. MURRAY. Down, September 16, 1876.
My dear Sir,
I have just received proofs in sheet of five sheets, so you will have to decide soon how many copies will have to be struck off. I do not know what to advise. The greater part of the book is extremely dry, and the whole on a special subject. Nevertheless, I am convinced that the book is of value, and I am convinced that for MANY years copies will be occasionally sold. Judging from the sale of my former books, and from supposing that some persons will purchase it to complete the set of my works, I would suggest 1500. But you must be guided by your larger experience. I will only repeat that I am convinced the book is of some permanent value...
CHARLES DARWIN TO VICTOR CARUS. Down, September 27, 1876.
My dear Sir,
I sent by this morning's post the four first perfect sheets of my new book, the title of which you will see on the first page, and which will be published early in November.
I am sorry to say that it is only shorter by a few pages than my 'Insectivorous Plants.' The whole is now in type, though I have corrected finally only half the volume. You will, therefore, rapidly receive the remainder. The book is very dull. Chapters II. to VI., inclusive, are simply a record of experiments. Nevertheless, I believe (though a man can never judge his own books) that the book is valuable. You will have to decide whether it is worth translating. I hope so. It has cost me very great labour, and the results seem to me remarkable and well established.
If you translate it, you could easily get aid for Chapters II. to VI., as there is here endless, but I have thought necessary repetition. I shall be anxious to hear what you decide...
I most sincerely hope that your health has been fairly good this summer.
My dear Sir, yours very truly, CH. DARWIN.
CHARLES DARWIN TO ASA GRAY. Down, October 28, 1876.
My dear Gray,
I send by this post all the clean sheets as yet printed, and I hope to send the remainder within a fortnight. Please observe that the first six chapters are not readable, and the six last very dull. Still I believe that the results are valuable. If you review the book, I shall be very curious to see what you think of it, for I care more for your judgment than for that of almost any one else. I know also that you will speak the truth, whether you approve or disapprove. Very few will take the trouble to read the book, and I do not expect you to read the whole, but I hope you will read the latter chapters.
... I am so sick of correcting the press and licking my horrid bad style into intelligible English.
[The 'Effects of Cross and Self-fertilisation' was published on November 10, 1876, and 1500 copies were sold before the end of the year. The following letter refers to a review in 'Nature' (February 15, 1877.):]
CHARLES DARWIN TO W. THISELTON DYER. Down, February 16, 1877.
Dear Dyer,
I must tell you how greatly I am pleased and honoured by your article in 'Nature,' which I have just read. You are an adept in saying what will please an author, not that I suppose you wrote with this express intention. I should be very well contented to deserve a fraction of your praise. I have also been much interested, and this is better than mere pleasure, by your argument about the separation of the sexes. I dare say that I am wrong, and will hereafter consider what you say more carefully: but at present I cannot drive out of my head that the sexes must have originated from two individuals, slightly different, which conjugated. But I am aware that some cases of conjugation are opposed to any such views.
With hearty thanks, Yours sincerely, CHARLES DARWIN.
CHAPTER 2.XII. — 'DIFFERENT FORMS OF FLOWERS ON PLANTS OF THE SAME SPECIES.'
1877
[The volume bearing the above title was published in 1877, and was dedicated by the author to Professor Asa Gray, "as a small tribute of respect and affection." It consists of certain earlier papers re-edited, with the addition of a quantity of new matter. The subjects treated in the book are: —
1. Heterostyled Plants.
2. Polygamous, Dioecious, and Gynodioecious Plants.
3. Cleistogamic Flowers.
The nature of heterostyled plants may be illustrated in the primrose, one of the best known examples of the class. If a number of primroses be gathered, it will be found that some plants yield nothing but "pin-eyed" flowers, in which the style (or organ for the transmission of the pollen to the ovule) is long, while the others yield only "thrum-eyed" flowers with short styles. Thus primroses are divided into two sets or castes differing structurally from each other. My father showed that they also differ sexually, and that in fact the bond between the two castes more nearly resembles that between separate sexes than any other known relationship. Thus for example a long-styled primrose, though it can be fertilised by its own pollen, is not FULLY fertile unless it is impregnated by the pollen of a short-styled flower. Heterostyled plants are comparable to hermaphrodite animals, such as snails, which require the concourse of two individuals, although each possesses both the sexual elements. The difference is that in the case of the primrose it is PERFECT FERTILITY, and not simply FERTILITY, that depends on the mutual action of the two sets of individuals.
The work on heterostyled plants has a special bearing, to which the author attached much importance, on the problem of origin of species. (See 'Autobiography,' volume i.)
He found that a wonderfully close parallelism exists between hybridisation and certain forms of fertilisation among heterostyled plants. So that it is hardly an exaggeration to say that the "illegitimately" reared seedlings are hybrids, although both their parents belong to identically the same species. In a letter to Professor Huxley, my father writes as if his researches on heterostyled plants tended to make him believe that sterility is a selected or acquired quality. But in his later publications, e.g. in the sixth edition of the 'Origin,' he adheres to the belief that sterility is an incidental rather than a selected quality. The result of his work on heterostyled plants is of importance as showing that sterility is no test of specific distinctness, and that it depends on differentiation of the sexual elements which is independent of any racial difference. I imagine that it was his instinctive love of making out a difficulty which to a great extent kept him at work so patiently on the heterostyled plants. But it was the fact that general conclusions of the above character could be drawn from his results which made him think his results worthy of publication. (See 'Forms of Flowers,' page 243.)
The papers which on this subject preceded and contributed to 'Forms of Flowers' were the following: —
"On the two Forms or Dimorphic Condition in the Species of Primula, and on their remarkable Sexual Relations." Linn. Soc. Journal, 1862.)
"On the Existence of Two Forms, and on their Reciprocal Sexual Relations, in several Species of the Genus Linum." Linn. Soc. Journal, 1863.
"On the Sexual Relations of the Three Forms of Lythrum salicaria," Ibid. 1864.
"On the Character and Hybrid-like Nature of the Offspring from the Illegitimate Unions of Dimorphic and Trimorphic Plants." Ibid. 1869.
"On the Specific Differences between Primula veris, Brit. Fl. (var. Officinalis, Linn.), P. vulgaris, Brit. Fl. (var. acaulis, Linn.) and P. elatior, Jacq.; and on the Hybrid Nature of the Common Oxlip. With Supplementary Remarks on Naturally Produced Hybrids in the Genus Verbascum." Ibid. 1869.
The following letter shows that he began the work on heterostyled plants with an erroneous view as to the meaning of the facts.]
CHARLES DARWIN TO J.D. HOOKER. Down, May 7 [1860].
... I have this morning been looking at my experimental cowslips, and I find some plants have all flowers with long stamens and short pistils, which I will call "male plants," others with short stamens and long pistils, which I will call "female plants." This I have somewhere seen noticed, I think by Henslow; but I find (after looking at my two sets of plants) that the stigmas of the male and female are of slightly different shape, and certainly different degree of roughness, and what has astonished me, the pollen of the so-called female plant, though very abundant, is more transparent, and each granule is exactly only 2/3 of the size of the pollen of the so-called male plant. Has this been observed? I cannot help suspecting [that] the cowslip is in fact dioecious, but it may turn out all a blunder, but anyhow I will mark with sticks the so-called male and female plants and watch their seeding. It would be a fine case of gradation between an hermaphrodite and unisexual condition. Likewise a sort of case of balancement of long and short pistils and stamens. Likewise perhaps throws light on oxlips...
I have now examined primroses and find exactly the same difference in the size of the pollen, correlated with the same difference in the length of the style and roughness of the stigmas.
CHARLES DARWIN TO ASA GRAY. June 8 [1860].
... I have been making some little trifling observations which have interested and perplexed me much. I find with primroses and cowslips, that about an equal number of plants are thus characterised.
SO-CALLED (by me) MALE plant. Pistil much shorter than stamens; stigma rather smooth, — POLLEN GRAINS LARGE, throat of corolla short.
SO-CALLED FEMALE plant. Pistil much longer than stamens, stigma rougher, POLLEN-GRAINS SMALLER, — throat of corolla long.
I have marked a lot of plants, and expected to find the so-called male plant barren; but judging from the feel of the capsules, this is not the case, and I am very much surprised at the difference in the size of the pollen... If it should prove that the so-called male plants produce less seed than the so-called females, what a beautiful case of gradation from hermaphrodite to unisexual condition it will be! If they produce about equal number of seed, how perplexing it will be.
CHARLES DARWIN TO J.D. HOOKER. Down, December 17 [1860?].
... I have just been ordering a photograph of myself for a friend; and have ordered one for you, and for heaven's sake oblige me, and burn that now hanging up in your room. — It makes me look atrociously wicked.
... In the spring I must get you to look for long pistils and short pistils in the rarer species of Primula and in some allied Genera. It holds with P. Sinensis. You remember all the fuss I made on this subject last spring; well, the other day at last I had time to weigh the seeds, and by Jove the plants of primroses and cowslip with short pistils and large grained pollen (Thus the plants which he imagined to be tending towards a male condition were more productive than the supposed females.) are rather more fertile than those with long pistils, and small-grained pollen. I find that they require the action of insects to set them, and I never will believe that these differences are without some meaning.
Some of my experiments lead me to suspect that the large-grained pollen suits the long pistils and the small-grained pollen suits the short pistils; but I am determined to see if I cannot make out the mystery next spring.
How does your book on plants brew in your mind? Have you begun it?..
Remember me most kindly to Oliver. He must be astonished at not having a string of questions, I fear he will get out of practice!
[The Primula-work was finished in the autumn of 1861, and on November 8th he wrote to Sir J.D. Hooker: —
"I have sent my paper on dimorphism in Primula to the Linn. Soc. I shall go up and read it whenever it comes on; I hope you may be able to attend, for I do not suppose many will care a penny for the subject."
With regard to the reading of the paper (on November 21st), he wrote to the same friend: —
"I by no means thought that I produced a "tremendous effect" in the Linn. Soc., but by Jove the Linn. Soc. produced a tremendous effect on me, for I could not get out of bed till late next evening, so that I just crawled home. I fear I must give up trying to read any paper or speak; it is a horrid bore, I can do nothing like other people."
To Dr. Gray he wrote, (December 1861): —
"You may rely on it, I will send you a copy of my Primula paper as soon as I can get one; but I believe it will not be printed till April 1st, and therefore after my Orchid Book. I care more for your and Hooker's opinion than for that of all the rest of the world, and for Lyell's on geological points. Bentham and Hooker thought well of my paper when read; but no one can judge of evidence by merely hearing a paper."
The work on Primula was the means of bringing my father in contact with the late Mr. John Scott, then working as a gardener in the Botanic Gardens at Edinburgh, — an employment which he seems to have chosen in order to gratify his passion for natural history. He wrote one or two excellent botanical papers, and ultimately obtained a post in India. (While in India he made some admirable observations on expression for my father.) He died in 1880.
A few phrases may be quoted from letters to Sir J.D. Hooker, showing my father's estimate of Scott: —
"If you know, do please tell me who is John Scott of the Botanical Gardens of Edinburgh; I have been corresponding largely with him; he is no common man."
"If he had leisure he would make a wonderful observer; to my judgment I have come across no one like him."
"He has interested me strangely, and I have formed a very high opinion of his intellect. I hope he will accept pecuniary assistance from me; but he has hitherto refused." (He ultimately succeeded in being allowed to pay for Mr. Scott's passage to India.)
"I know nothing of him excepting from his letters; these show remarkable talent, astonishing perseverance, much modesty, and what I admire, determined difference from me on many points."
So highly did he estimate Scott's abilities that he formed a plan (which however never went beyond an early stage of discussion) of employing him to work out certain problems connected with intercrossing.
The following letter refers to my father's investigations on Lythrum (He was led to this, his first case of trimorphism by Lecoq's 'Geographie Botanique,' and this must have consoled him for the trick this work played him in turning out to be so much larger than he expected. He wrote to Sir J.D. Hooker: "Here is a good joke: I saw an extract from Lecoq, 'Geograph. Bot.,' and ordered it and hoped that it was a good sized pamphlet, and nine thick volumes have arrived!"), a plant which reveals even a more wonderful condition of sexual complexity than that of Primula. For in Lythrum there are not merely two, but three castes, differing structurally and physiologically from each other:]
CHARLES DARWIN TO ASA GRAY. Down, August 9 [1862].
My dear Gray,
It is late at night, and I am going to write briefly, and of course to beg a favour.
The Mitchella very good, but pollen apparently equal-sized. I have just examined Hottonia, grand difference in pollen. Echium vulgare, a humbug, merely a case like Thymus. But I am almost stark staring mad over Lythrum (On another occasion he wrote (to Dr. Gray) with regard to Lythrum: "I must hold hard, otherwise I shall spend my life over dimorphism."); if I can prove what I fully believe, it is a grand case of TRIMORPHISM, with three different pollens and three stigmas; I have castrated and fertilised above ninety flowers, trying all the eighteen distinct crosses which are possible within the limits of this one species! I cannot explain, but I feel sure you would think it a grand case. I have been writing to Botanists to see if I can possibly get L. hyssopifolia, and it has just flashed on me that you might have Lythrum in North America, and I have looked to your Manual. For the love of heaven have a look at some of your species, and if you can get me seed, do; I want much to try species with few stamens, if they are dimorphic; Nesaea verticillata I should expect to be trimorphic. Seed! Seed! Seed! I should rather like seed of Mitchella. But oh, Lythrum!
Your utterly mad friend, C. DARWIN.
P.S. — There is reason in my madness, for I can see that to those who already believe in change of species, these facts will modify to a certain extent the whole view of Hybridity. (A letter to Dr. Gray (July, 1862) bears on this point: "A few days ago I made an observation which has surprised me more than it ought to do — it will have to be repeated several times, but I have scarcely a doubt of its accuracy. I stated in my Primula paper that the long-styled form of Linum grandiflorum was utterly sterile with its own pollen; I have lately been putting the pollen of the two forms on the stigma of the SAME flower; and it strikes me as truly wonderful, that the stigma distinguishes the pollen; and is penetrated by the tubes of the one and not by those of the other; nor are the tubes exserted. Or (which is the same thing) the stigma of the one form acts on and is acted on by pollen, which produces not the least effect on the stigma of the other form. Taking sexual power as the criterion of difference, the two forms of this one species may be said to be generically distinct.")
[On the same subject he wrote to Sir Joseph Hooker in August 1862: —
"Is Oliver at Kew? When I am established at Bournemouth I am completely mad to examine any fresh flowers of any Lythraceous plant, and I would write and ask him if any are in bloom."
Again he wrote to the same friend in October: —
"If you ask Oliver, I think he will tell you I have got a real odd case in Lythrum, it interests me extremely, and seems to me the strangest case of propagation recorded amongst plants or animals, viz. a necessary triple alliance between three hermaphrodites. I feel sure I can now prove the truth of the case from a multitude of crosses made this summer."
In an article, 'Dimorphism in the Genitalia of Plants' ('Silliman's Journal,' 1862, volume xxxiv. page 419), Dr. Gray pointed out that the structural difference between the two forms of Primula had already been defined in the 'Flora of North America,' as DIOECIO-DIMORPHISM. The use of this term called forth the following remarks from my father. The letter also alludes to a review of the 'Fertilisation of Orchids' in the same volume of 'Silliman's Journal.']
CHARLES DARWIN TO ASA GRAY. Down, November 26 [1862].
My dear Gray,
The very day after my last letter, yours of November 10th, and the review in 'Silliman,' which I feared might have been lost, reached me. We were all very much interested by the political part of your letter; and in some odd way one never feels that information and opinions painted in a newspaper come from a living source; they seem dead, whereas all that you write is full of life. The reviews interested me profoundly; you rashly ask for my opinion, and you must consequently endure a long letter. First for Dimorphism; I do not AT PRESENT like the term "Dioecio-dimorphism;" for I think it gives quite a false notion, that the phenomena are connected with a separation of the sexes. Certainly in Primula there is unequal fertility in the two forms, and I suspect this is the case with Linum; and, therefore I felt bound in the Primula paper to state that it might be a step towards a dioecious condition; though I believe there are no dioecious forms in Primulaceae or Linaceae. But the three forms in Lythrum convince me that the phenomenon is in no way necessarily connected with any tendency to separation of sexes. The case seems to me in result or function to be almost identical with what old C.K. Sprengel called "dichogamy," and which is so frequent in truly hermaphrodite groups; namely, the pollen and stigma of each flower being mature at different periods. If I am right, it is very advisable not to use the term "dioecious," as this at once brings notions of separation of sexes.
