THE botanical work which my father accomplished by the guidance of the light cast on the study of natural history by his own work on evolution remains to be noticed. In a letter to Mr. Murray, September 24th, 1861, speaking of his book the Fertilisation of Orchids, he says: “It will perhaps serve to illustrate how Natural History may be worked under the belief of the modification of species” This remark gives a suggestion as to the value and interest of his botanical work, and it might be expressed in far more emphatic language without danger of exaggeration.
In the same letter to Mr. Murray, he says: “I think this little volume will do good to the Origin, as it will show that I have worked hard at details.” It is true that his botanical work added a mass of corroborative detail to the case for Evolution, but the chief support given to his doctrines by these researches was of another kind. They supplied an argument against those critics who have so freely dogmatised as to the uselessness of particular structures, and as to the consequent impossibility of their having been developed by means of natural selection. His observations on Orchids enabled him to say: “I can show the meaning of some of the apparently meaningless ridges and horns; who will now venture to say that this or that structure is useless?” A kindred point is expressed in a letter to Sir J. D. Hooker (May 14th, 1862):—
“When many parts of structure, as in the woodpecker, show distinct adaptation to external bodies, it is preposterous to attribute them to the effects of climate, &c., but when a single point alone, as a hooked seed, it is conceivable it may thus have arisen. I have found the study of Orchids eminently useful in showing me how nearly all parts of the flower are co-adapted for fertilisation by insects, and therefore the results of natural selection,—even the most trifling details of structure.”
One of the greatest services rendered by my father to the study of Natural History is the revival of Teleology. The evolutionist studies the purpose or meaning of organs with the zeal of the older Teleologist, but with far wider and more coherent purpose. He has the invigorating knowledge that he is gaining not isolated conceptions of the economy of the present, but a coherent view of both past and present. And even where he fails to discover the use of any part, he may, by a knowledge of its structure, unravel the history of the past vicissitudes in the life of the species. In this way a vigour and unity is given to the study of the forms of organised beings, which before it lacked. Mr. Huxley has well remarked:* “Perhaps the most remarkable service to the philosophy of Biology rendered by Mr. Darwin is the reconciliation of Teleology and Morphology, and the explanation of the facts of both, which his views offer. The teleology which supposes that the eye, such as we see it in man, or one of the higher vertebrata, was made with the precise structure it exhibits, for the purpose of enabling the animal which possesses it to see, has undoubtedly received its death-blow. Nevertheless, it is necessary to remember that there is a wider teleology which is not touched by the doctrine of Evolution, but is actually based upon the fundamental proposition of Evolution.”
The point which here especially concerns us is to recognise that this “great service to natural science,” as Dr. Gray describes it, was effected almost as much by Darwin’s special botanical work as by the Origin of Species.
For a statement of the scope and influence of my father’s botanical work, I may refer to Mr. Thiselton Dyer’s article in ‘Charles Darwin,’ one of the Nature Series. Mr. Dyer’s wide knowledge, his friendship with my father, and his power of sympathising with the work of others, combine to give this essay a permanent value. The following passage (p. 43) gives a true picture:—
“Notwithstanding the extent and variety of his botanical work, Mr. Darwin always disclaimed any right to be regarded as a professed botanist. He turned his attention to plants, doubtless because they were convenient objects for studying organic phenomena in their least complicated forms; and this point of view, which, if one may use the expression without disrespect, had something of the amateur about it, was in itself of the greatest importance. For, from not being, till he took up any point, familiar with the literature bearing on it, his mind was absolutely free from any prepossession. He was never afraid of his facts, or of framing any hypothesis, however startling, which seemed to explain them. ... In any one else such an attitude would have produced much work that was crude and rash. But Mr. Darwin—if one may venture on language which will strike no one who had conversed with him as over-strained —seemed by gentle persuasion to have penetrated that reserve of nature which baffles smaller men. In other words, his long experience had given him a kind of instinctive insight into the method of attack of any biological problem, however unfamiliar to him, while he rigidly controlled the fertility of his mind in hypothetical explanations by the no less fertility of ingeniously devised experiment.”
To form any just idea of the greatness of the revolution worked by my father’s researches in the study of the fertilisation of flowers, it is necessary to know from what a condition this branch of knowledge has emerged. It should be remembered that it was only during the early years of the present century that the idea of sex, as applied to plants, became firmly established. Sachs, in his History of Botany * (1875), has given some striking illustrations of the remarkable slowness with which its acceptance gained ground. He remarks that when we consider the experimental proofs given by Camerarius (1694), and by Kölreuter (1761-66), it appears incredible that doubts should afterwards have been raised as to the sexuality of plants. Yet he shows that such doubts did actually repeatedly crop up. These adverse criticisms rested for the most part on careless experiments, but in many cases on a priori arguments. Even as late as 1820, a book of this kind, which would now rank with circle squaring, or flat-earth philosophy, was seriously noticed in a botanical journal. A distinct conception of sex, as applied to plants, had, in fact, not long emerged from the mists of profitless discussion and feeble experiment, at the time when my father began botany by attending Henslow’s lectures at Cambridge.
When the belief in the sexuality of plants had become established as an incontrovertible piece of knowledge, a weight of misconception remained, weighing down any rational view of the subject. Camerarius* believed (naturally enough in his day) that hermaphrodite † flowers are necessarily self-fertilised. He had the wit to be astonished at this, a degree of intelligence which, as Sachs points out, the majority of his successors did not attain to.
The following extracts from a note-book show that this point occurred to my father as early as 1837:
“Do not plants which have male and female organs together [i.e. in the same flower] yet receive influence from other plants? Does not Lyell give some argument about varieties being difficult to keep [true] on account of pollen from other plants? Because this may be applied to show all plants do receive intermixture”
Sprengel, ‡ indeed, understood that the hermaphrodite structure of flowers by no means necessarily leads to self-fertilisation. But although he discovered that in many cases pollen is of necessity carried to the stigma of another flower, he did not understand that in the advantage gained by the intercrossing of distinct plants lies the key to the whole question. Hermann Müller# has well remarked that this “omission was for several generations fatal to Sprengel’s work. . . . For both at the time and subsequently, botanists felt above all the weakness of his theory, and they set aside, along with his defective ideas, the rich store of his patient and acute observations and his comprehensive and accurate interpretations.” It remained for my father to convince the world that the meaning hidden in the structure of flowers was to be found by seeking light in the same direction in which Sprengel, seventy years before, had laboured. Robert Brown was the connecting link between them, for it was at his recommendation that my father in 1841 read Sprengel’s now celebrated Secret of Nature Displayed. ||
The book impressed him as being “full of truth,” although “with some little nonsense.” It not only encouraged him in kindred speculation, but guided him in his work, for in 1844 he speaks of verifying Sprengel’s observations. It may be doubted whether Robert Brown ever planted a more fruitful seed than in putting such a book into such hands.
A passage in the Autobiography (p. 44) shows how it was that my father was attracted to the subject of fertilisation: “During the summer of 1839, and I believe during the previous summer, I was led to attend to the cross-fertilisation of flowers by the aid of insects, from having come to the conclusion in my speculations on the origin of species, that crossing played an important part in keeping specific forms constant.”
The original connection between the study of flowers and the problem of evolution is curious, and could hardly have been predicted. Moreover, it was not a permanent bond. My father proved by a long series of laborious experiments, that when a plant is fertilised and sets seeds under the influence of pollen from a distinct individual, the offspring so produced are superior in vigour to the offspring of self-fertilisation, i.e. of the union of the male and female elements of a single plant. When this fact was established, it was possible to understand the raison d’être of the machinery which insures cross-fertilisation in so many flowers; and to understand how natural selection can act on, and mould, the floral structure.
Asa Gray has well remarked with regard to this central idea (Nature, June 4, 1874):—“The aphorism, ‘Nature abhors a vacuum,’ is a characteristic specimen of the science of the middle ages. The aphorism, ‘Nature abhors close fertilisation,’ and the demonstration of the principle, belong to our age and to Mr. Darwin. To have originated this, and also the principle of Natural Selection . . . and to have applied these principles to the system of nature, in such a manner as to make, within a dozen years, a deeper impression upon natural history than has been made since Linnæus, is ample title for one man’s fame.”
The flowers of the Papilionaceæ * attracted his attention early, and were the subject of his first paper on fertilisation.† The following extract from an undated letter to Asa Gray seems to have been written before the publication of this paper, probably in 1856 or 1857:—
“... What you say on Papilionaceous flowers is very true; and I have no facts to show that varieties are crossed; but yet (and the same remark is applicable in a beautiful way to Fumaria and Dielytra, as I noticed many years ago), I must believe that the flowers are constructed partly in direct relation to the visits of insects; and how insects can avoid bringing pollen from other individuals I cannot understand. It is really pretty to watch the action of a humble-bee on the scarlet kidney bean, and in this genus (and in Lathyrus grandiflorus) * the honey is so placed that the bee invariably alights on that one side of the flower towards which the spiral pistil is protruded (bringing out with it pollen), and by the depression of the wing-petal is forced against the bee’s side all dusted with pollen. In the broom the pistil is rubbed on the centre of the back of the bee. I suspect there is something to be made out about the Leguminosæ, which will bring the case within our theory; though I have failed to do so. Our theory will explain why in the vegetable . . . kingdom the act of fertilisation even in hermaphrodites usually takes place sub jove, though thus exposed to great injury from damp and rain.”
A letter to Dr. Asa Gray (September 5th, 1857) gives the substance of the paper in the Gardeners’ Chronicle,:—
“Lately I was led to examine buds of kidney bean with the pollen shed; but I was led to believe that the pollen could hardly get on the stigma by wind or otherwise, except by bees visiting [the flower] and moving the wing petals: hence I included a small bunch of flowers in two bottles in every way treated the same: the flowers in one I daily just momentarily moved, as if by a bee; these set three fine pods, the other not one. Of course this little experiment must be tried again, and this year in England it is too late, as the flowers seem now seldom to set. If bees are necessary to this flower’s self-fertilisation, bees must almost cross them, as their dusted right-side of head and right legs constantly touch the stigma.
“I have, also, lately been reobserving daily Lobelia fulgens— this in my garden is never visited by insects, and never sets seeds, without pollen be put on the stigma (whereas the small blue Lobelia is visited by bees and does set seed); I mention this because there are such beautiful contrivances to prevent the stigma ever getting its own pollen; which seems only explicable on the doctrine of the advantage of crosses.”
of “over-time” work. He wrote to a friend, “that confounded Leguminous paper was done in the afternoon, and the consequence was I had to go to Moor park for a week.”
The paper was supplemented by a second in 1858.* The chief object of these publications seems to have been to obtain information as to the possibility of growing varieties of Leguminous plants near each other, and yet keeping them true. It is curious that the Papilionaceæ should not only have been the first flowers which attracted his attention by their obvious adaptation to the visits of insects, but should also have constituted one of his sorest puzzles. The common pea and the sweet pea gave him much difficulty, because, although they are as obviously fitted for insect-visits as the rest of the order, yet their varieties keep true. The fact is that neither of these plants being indigenous, they are not perfectly adapted for fertilisation by British insects. He could not, at this stage of his observations, know that the co-ordination between a flower and the particular insect which fertilises it may be as delicate as that between a lock and its key, so that this explanation was not likely to occur to him.
Besides observing the Leguminosæ, he had already begun, as shown in the foregoing extracts, to attend to the structure of other flowers in relation to insects. At the beginning of 1860 he worked at Leschenaultia,† which at first puzzled him, but was ultimately made out. A passage in a letter chiefly relating to Leschenaultia seems to show that it was only in the spring of 1860 that he began widely to apply his knowledge to the relation of insects to other flowers. This is somewhat surprising, when we remember that he had read Sprengel many years before. He wrote (May 14):—
“I should look at this curious contrivance as specially related to visits of insects; as I begin to think is almost universally the case.”
Even in July 1862 he wrote to Asa Gray:
“There is no end to the adaptations. Ought not these cases to make one very cautious when one doubts about the use of all parts? I fully believe that the structure of all irregular flowers is governed in relation to insects. Insects are the Lords of the floral (to quote the witty Athenœum) world.”
This idea has been worked out by H. Müller, who has written on insects in the character of flower-breeders or flower-fanciers, showing how the habits and structure of the visitors are reflected in the forms and colours of the flowers visited.
He was probably attracted to the study of Orchids by the fact that several kinds are common near Down. The letters of 1860 show that these plants occupied a good deal of his attention; and in 1861 he gave part of the summer and all the autumn to the subject. He evidently considered himself idle for wasting time on Orchids which ought to have been given to Variation under Domestication. Thus he wrote:—
“There is to me incomparably more interest in observing than in writing; but I feel quite guilty in trespassing on these subjects, and not sticking to varieties of the confounded cocks, hens and ducks. I hear that Lyell is savage at me.”
It was in the summer of 1860 that he made out one of the most striking and familiar facts in the Orchid-book, namely, the manner in which the pollen masses are adapted for removal by insects. He wrote to Sir J. D. Hooker, July 12:—
“I have been examining Orchis pyramidalis, and it almost equals, perhaps even beats, your Listera case; the sticky glands are congenitally united into a saddle-shaped organ, which has great power of movement, and seizes hold of a bristle (or proboscis) in an admirable manner, and then another movement takes place in the pollen masses, by which they are beautifully adapted to leave pollen on the two lateral stigmatic surfaces. I never saw anything so beautiful.”
In June of the same year he wrote:—
“You speak of adaptation being rarely visible, though present in plants. I have just recently been looking at the common Orchis, and I declare I think its adaptations in every part of the flower quite as beautiful and plain, or even more beautiful than in the woodpecker.” *
He wrote also to Dr. Gray, June 8, 1860:—
“Talking of adaptation, I have lately been looking at our common orchids, and I dare say the facts are as old and well-known as the hills, but I have been so struck with admiration at the contrivances, that I have sent a notice to the Gardeners’ Chronicle”
Besides attending to the fertilisation of the flowers he was already, in 1860, busy with the homologies of the parts, a subject of which he made good use in the Orchid book. He wrote to Sir Joseph Hooker (July):—
“It is a real good joke my discussing homologies of Orchids with you, after examining only three or four genera; and this very fact makes me feel positive I am right! I do not quite understand some of your terms; but sometime I must get you to explain the homologies; for I am intensely interested in the subject, just as at a game of chess.”
This work was valuable from a systematic point of view. In 1880 he wrote to Mr. Bentham:—
“It was very kind in you to write to me about the Orchideæ, for it has pleased me to an extreme degree that I could have been of the least use to you about the nature of the parts.”
The pleasure which his early observations on Orchids gave him is shown in such passages as the following from a letter to Sir J. D. Hooker (July 27, 1861):—
“You cannot conceive how the Orchids have delighted me. They came safe, but box rather smashed; cylindrical old cocoa- or snuff-canister much safer. I enclose postage. As an account of the movement, I shall allude to what I suppose is Oncidium, to make certain,—is the enclosed flower with crumpled petals this genus? Also I most specially want to know what the enclosed little globular brown Orchid is. I have only seen pollen of a Cattleya on a bee, but surely have you not unintentionally sent me what I wanted most (after Catasetum or Mormodes), viz., one of the Epidendreæ? ! I particularly want (and will presently tell you why) another spike of this little Orchid, with older flowers, some even almost withered.”
His delight in observation is again shown in a letter to Dr. Gray (1863). Referring to Crüger’s letters from Trinidad, he wrote:—“Happy man, he has actually seen crowds of bees flying round Catasetum, with the pollinia sticking to their backs!”
The following extracts of letters to Sir J. D. Hooker illustrate further the interest which his work excited in him:—
“Veitch sent me a grand lot this morning. What wonderful structures!
“I have now seen enough, and you must not send me more, for though I enjoy looking at them much, and it has been very useful to me, seeing so many different forms, it is idleness. For my object each species requires studying for days. I wish you had time to take up the group. I would give a good deal to know what the rostellum is, of which I have traced so many curious modifications. I suppose it cannot be one of the stigmas,* there seems a great tendency for two lateral stigmas to appear. My paper, though touching on only subordinate points will run, I fear, to 100 MS. folio pages ! The beauty of the adaptation of parts seems to me unparalleled. I should think or guess waxy pollen was most differentiated. In Cypripedium which seems least modified, and a much exterminated group, the grains are single. In all others, as far as I have seen, they are in packets of four; and these packets cohere into many wedge-formed masses in Orchis; into eight, four, and finally two. It seems curious that a flower should exist, which could at most fertilise only two other flowers, seeing how abundant pollen generally is; this fact I look at as explaining the perfection of the contrivance by which the pollen, so important from its fewness, is carried from flower to flower” † (1861).
“I was thinking of writing to you to-day, when your note with the Orchids came. What frightful trouble you have taken about Vanilla; you really must not take an atom more; for the Orchids are more play than real work. I have been much interested by Epidendrum, and have worked all morning at them; for Heaven’s sake, do not corrupt me by any more” (August 30, 1861).
He originally intended to publish his notes on Orchids as a paper in the Linnean Society’s Journal, but it soon became evident that a separate volume would be a more suitable form of publication. In a letter to Sir J. D. Hooker, Sept. 24, 1861, he writes:—
“I have been acting, I fear that you will think, like a goose; and perhaps in truth I have. When I finished a few days ago my Orchis paper, which turns out one hundred and forty folio pages !! and thought of the expense of woodcuts, I said to myself, I will offer the Linnean Society to withdraw it, and publish it in a pamphlet. It then flashed on me that perhaps Murray would publish it, so I gave him a cautious description, and offered to share risks and profits. This morning he writes that he will publish and take all risks, and share profits and pay for all illustrations. It is a risk, and Heaven knows whether it will not be a dead failure, but I have not deceived Murray, and [have] told him that it would interest those alone who cared much for natural history. I hope I do not exaggerate the curiosity of the many special contrivances.”
And again on September 28th:—
“What a good soul you are not to sneer at me, but to pat me on the back. I have the greatest doubt whether I am not going to do, in publishing my paper, a most ridiculous thing. It would annoy me much, but only for Murray’s sake, if the publication were a dead failure.”
There was still much work to be done, and in October he was still receiving Orchids from Kew, and wrote to Hooker:—
“It is impossible to thank you enough. I was almost mad at the wealth of Orchids.” And again—
“Mr. Veitch most generously has sent me two splendid buds of Mormodes, which will be capital for dissection, but I fear will never be irritable; so for the sake of charity and love of heaven do, I beseech you, observe what movement takes place in Cychnoches, and what part must be touched. Mr. V. has also sent me one splendid flower of Catasetum, the most wonderful Orchid I have seen”
On October 13 he wrote to Sir Joseph Hooker:—
“It seems that I cannot exhaust your good nature. I have had the hardest day’s work at Catasetum and buds of Mormodes, and believe I understand at last the mechanism of movements and the functions. Catasetum is a beautiful case of slight modification of structure leading to new functions. I never was more interested in any subject in all my life than in this of Orchids. I owe very much to you.”
Again to the same friend, November 1, 1861:—
“If you really can spare another Catasetum, when nearly ready, I shall be most grateful; had I not better send for it? The case is truly marvellous; the (so-called) sensation, or stimulus from a light touch is certainly transmitted through the antennæ for more than one inch instantaneously. ... A cursed insect or something let my last flower off last night.”
Professor de Candolle has remarked * of my father, “Ce n’est pas lui qui aurait demandé de construire des palais pour y loger des laboratoires.” This was singularly true of his orchid work, or rather it would be nearer the truth to say that he had no laboratory, for it was only after the publication of the Fertilisation of Orchids, that he built himself a green-house. He wrote to Sir J. D. Hooker (December 24th, 1862):—
“And now I am going to tell you a most important piece of news!! I have almost resolved to build a small hothouse; my neighbour’s really first-rate gardener has suggested it, and offered to make me plans, and see that it is well done, and he is really a clever fellow, who wins lots of prizes, and is very observant. He believes that we should succeed with a little patience; it will be a grand amusement for me to experiment with plants”
Again he wrote (February 15th, 1863):—
“I write now because the new hot-house is ready, and I long to stock it, just like a schoolboy. Could you tell me pretty soon what plants you can give me; and then I shall know what to order? And do advise me how I had better get such plants as you can spare. Would it do to send my tax-cart early in the morning, on a day that was not frosty, lining the cart with mats, and arriving here before night? I have no idea whether this degree of exposure (and of course the cart would be cold) could injure stove-plants; they would be about five hours (with bait) on the journey home”
A week later he wrote:—
“You cannot imagine what pleasure your plants give me (far more than your dead Wedgwood-ware can give you); H. and I go and gloat over them, but we privately confessed to each other, that if they were not our own, perhaps we should not see such transcendant beauty in each leaf.”
And in March, when he was extremely unwell, he wrote:—
“A few words about the stove-plants; they do so amuse me. I have crawled to see them two or three times. Will you correct and answer, and return enclosed. I have hunted in all my books and cannot find these names, and I like much to know the family” His difficulty with regard to the names of plants is illustrated, with regard to a Lupine on which he was at work, in an extract from a letter (July 21, 1866) to Sir J. D. Hooker: “I sent to the nursery garden, whence I bought the seed, and could only hear that it was ‘the common blue Lupine,’ the man saying ‘he was no scholard, and did not know Latin, and that parties who make experiments ought to find out the names.’”
The book was published May 15th, 1862. Of its reception he writes to Mr. Murray, June 13th and 18th:—
“The Botanists praise my Orchid-book to the skies. Some one sent me (perhaps you) the Parthenon, with a good review. The Athenœum* treats me with very kind pity and contempt; but the reviewer knew nothing of his subject.”
“There is a superb, but I fear exaggerated, review in the London Review.† But I have not been a fool, as I thought I was, to publish; for Asa Gray, about the most competent judge in the world, thinks almost as highly of the book as does the London Review. The Athenœum will hinder the sale greatly.”
The Rev. M. J. Berkeley was the author of the notice in the London Review, as my father learned from Sir J. D. Hooker, who added, “I thought it very well done indeed. I have read a good deal of the Orchid-book, and echo all he says.”
To this my father replied (June 30th, 1862):—
“My dear old friend,—You speak of my warming the cockles of your heart, but you will never know how often you have warmed mine. It is not your approbation of my scientific work (though I care for that more than for any one’s) : it is something deeper. To this day I remember keenly a letter you wrote to me from Oxford, when I was at the Water-cure, and how it cheered me when I was utterly weary of life. Well, my Orchid-book is a success (but I do not know whether it sells).”
In another letter to the same friend, he wrote:—
“You have pleased me much by what you say in regard to Bentham and Oliver approving of my book; for I had got a sort of nervousness, and doubted whether I had not made an egregious fool of myself, and concocted pleasant little stinging remarks for reviews, such as ‘Mr. Darwin’s head seems to have been turned by a certain degree of success, and he thinks that the most trifling observations are worth publication.’”
He wrote too, to Asa Gray:—
“Your generous sympathy makes you over-estimate what you have read of my Orchid-book. But your letter of May 18th and 26th has given me an almost foolish amount of satisfaction. The subject interested me, I knew, beyond its real value; but I had lately got to think that I had made myself a complete fool by publishing in a semi-popular form. Now I shall confidently defy the world. . . . No doubt my volume contains much error: how curiously difficult it is to be accurate, though I try my utmost. Your notes have interested me beyond measure. I can now afford to d— my critics with ineffable complacency of mind. Cordial thanks for this benefit.”
Sir Joseph Hooker reviewed the book in the Gardeners’ Chronicle, writing in a successful imitation of the style of Lindley, the Editor. My father wrote to Sir Joseph (Nov. 12, 1862):—
“So you did write the review in the Gardeners’Chronicle. Once or twice I doubted whether it was Lindley; but when I came to a little slap at R. Brown, I doubted no longer. You arch-rogue! I do not wonder you have deceived others also. Perhaps I am a conceited dog; but if so, you have much to answer for; I never received so much praise, and coming from you I value it much more than from any other.”
With regard to botanical opinion generally, he wrote to Dr. Gray, “I am fairly astonished at the success of my book with botanists” Among naturalists who were not botanists, Lyell was pre-eminent in his appreciation of the book. I have no means of knowing when he read it, but in later life, as I learn from Professor Judd, he was enthusiastic in praise of the Fertilisation of Orchids, which he considered “next to the Origin, as the most valuable of all Darwin’s works” Among the general public the author did not at first hear of many disciples, thus he wrote to his cousin Pox in September 1862: “Hardly any one not a botanist, except yourself, as far as I know, has cared for it”
If we examine the literature relating to the fertilisation of flowers, we do not find that this new branch of study showed any great activity immediately after the publication of the Orchid-book. There a few papers by Asa Gray, in 1862 and 1863, by Hildebrand in 1864, and by Moggridge in 1865, but the great mass of work by Axell, Delpino, Hildebrand, and the Müllers, did not begin to appear until about 1867. The period during which the new views were being assimilated, and before they became thoroughly fruitful, was, however, surprisingly short. The later activity in this department may be roughly gauged by the fact that the valuable ‘Bibliography,’ given by Professor D’Arcy Thompson in his translation of Müller’s Befruchtung (1883),* contains references to 814 papers.
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 rewritten, and a large amount of new matter added, much of which the author owed to his friend Fritz Müller.
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.”
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.”
Two other books bearing on the problem of sex in plants require a brief notice. The Effects of Cross- and Self-Fertilisation, published in 1876, is one of his most important works, and at the same time one of the most unreadable to any but the professed naturalist. Its value lies in the proof it offers of the increased vigour given to the offspring by the act of cross-fertilisation. It is the complement of the Orchid book because it makes us understand the advantage gained by the mechanisms for insuring cross-fertilisation described in that work.
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 accompany asexual reproductions.
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. The plants were grown for the sake of some observations on inheritance, and not with any view to crossbreeding, 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, tha this attention was “thoroughly aroused,” and that he determined to make a series of experiments specially directed to the question.
The volume on Forms of flowers 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:—
(i.) Heterostyled Plants.
(ii.) Polygamous, Diœcious, and Gynodiœcious Plants.
(iii.) 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 the origin of species.*
He found that a wonderfully close parallelism exists between hybridisation (i.e. crosses between distinct species), 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, given in the second volume of the Life and Letters (p. 384), 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.
*The “Genealogy of Animals” (The Academy, 1869), reprinted in Critiques and Addresses.
* An English edition is published by the Clarendon Press, 1890.
* Sachs, Geschichte d. Botanik, p. 419.
† That is to say, flowers possessing both stamens, or male organs, and pistils or female organs.
‡ Christian Conrad Sprengel, born 1750, died 1816.
# Fertilisation of Flowers (Eng. Trans.) 1883, p. 3.
|| Das entdeckte Geheimniss der Natur im Baue und in der Befruchtung der Blumen. Berlin, 1793.
* The order to which the pea and bean belong.
† Gardeners’ Chronicle, 1857, p. 725. It appears that this paper was a piece
*The sweet pea and everlasting pea belong to the genus Lathyrus.
* Gardeners’ Chronicle, 1858, p. 828.
† He published a short paper on the manner of fertilisation of this flower, in the Gardeners’ Chronicle 1871, p. 1166.
* The woodpecker was one of his stock examples of adaptation.
* It is a modification of the upper stigma.
† This rather obscure statement may be paraphrased thus:—
The machinery is so perfect that the plant can afford to minimise the amount of pollen produced. Where the machinery for pollen distribution is of a cruder sort, for instance where it is carried by the wind, enormous quantities are produced, e. g. in the fir tree.
* “Darwin considéré, &c.,” Archives des Sciences Physiques et Naturellesɜème période. Tome vii. 481, 1882.
* May 24th, 1862
† June 14th, 1862.
* My father’s “Prefatory Notice” to this work is dated February 6th, 1882, and is therefore almost the last of his writings.
† The pollen or fertilising element is in each species adapted to produce a certain change in the egg-cell (or female element), just as a key is adapted to a lock. If a key opens a lock for which it was never intended it is an incidental result. In the same way if the pollen of species of A. proves to be capable of fertilising the egg-cell of species B. we may call it incidental.