FERTILISATION OF FLOWERS.
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:[269] "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_[270]
(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
Koelreuter (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[271] believed
(naturally enough in his day) that hermaphrodite[272] 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,[273] 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 Mueller[274] 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_.[275]
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'etre_ 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 Linnaeus, is ample title for one man's fame."
The flowers of the Papilionaceae[276] attracted his attention early, and
were the subject of his first paper on fertilisation.[277] 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_)[278] 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 Leguminosae, 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."
The paper was supplemented by a second in 1858.[279] 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 Papilionaceae 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 Leguminosae, 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,[280] 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 _Athenaeum_) world."
This idea has been worked out by H. Mueller, 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."[281]
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 Orchideae, for it has
pleased me to an extreme degree that I could have been of the _least_
use to you about the nature of the parts."
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 Epidendreae?! 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 Crueger'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,[282] 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"[283](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 antennae for more than one inch
_instantaneously_.... A cursed insect or something let my last flower
off last night."
Professor de Candolle has remarked[284] of my father, "Ce n'est pas lui
qui aurait demande 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 greenhouse. 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 hot-house; 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 follow, 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 _Athenaeum_[285]
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_.[286] 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
_Athenaeum_ 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 Fox 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 are 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 Muellers, 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 Mueller's _Befruchtung_ (1883),[287] 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
Mueller.
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."
_The Effect of Cross-and Self-fertilisation in the Vegetable Kingdom.
Different Forms of Flowers on Plants of the same species._
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
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 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, Dioecious, and Gynodioecious 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.[288]
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[289] 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.
FOOTNOTES:
[269] The "Genealogy of Animals" (_The Academy_, 1869), reprinted in
_Critiques and Addresses_.
[270] An English edition is published by the Clarendon Press, 1890.
[271] Sachs, _Geschichte d. Botanik_, p. 419.
[272] That is to say, flowers possessing both stamens, or male organs,
and pistils or female organs.
[273] Christian Conrad Sprengel, born 1750, died 1816.
[274] _Fertilisation of Flowers_ (Eng. Trans.) 1883, p. 3.
[275] _Das entdeckte Geheimniss der Natur im Baue und in der Befruchtung
der Blumen._ Berlin, 1793.
[276] The order to which the pea and bean belong.
[277] _Gardeners' Chronicle_, 1857, p. 725. It appears that this paper
was a piece 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."
[278] The sweet pea and everlasting pea belong to the genus Lathyrus.
[279] _Gardeners' Chronicle_, 1858, p. 828.
[280] He published a short paper on the manner of fertilisation of this
flower, in the _Gardeners' Chronicle_ 1871, p. 1166.
[281] The woodpecker was one of his stock examples of adaptation.
[282] It is a modification of the upper stigma.
[283] 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.
[284] "Darwin considere, &c.," _Archives des Sciences Physiques et
Naturelles_ 3eme periode. Tome vii. 481, 1882.
[285] May 24th, 1862.
[286] June 14th, 1862.
[287] My father's "Prefatory Notice" to this work is dated February 6th,
1882, and is therefore almost the last of his writings.
[288] See Autobiography, p. 48.
[289] 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.