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.
... I was much perplexed by Oliver's remarks in the 'Natural History
Review' on the Primula case, on the lower plants having sexes more often
separated than in the higher plants,--so exactly the reverse of what
takes place in animals. Hooker in his review of the 'Orchids' repeats
this remark. There seems to be much truth in what you say ("Forms which
are low in the scale as respects morphological completeness may be
high in the scale of rank founded on specialisation of structure and
function."--Dr. Gray, in 'Silliman's Journal.'), and it did not occur to
me, about no improbability of specialisation in CERTAIN lines in lowly
organised beings. I could hardly doubt that the hermaphrodite state is
the aboriginal one. But how is it in the conjugation of Confervae--is
not one of the two individuals here in fact male, and the other female?
I have been much puzzled by this contrast in sexual arrangements
between plants and animals. Can there be anything in the following
consideration: By ROUGHEST calculation about one-third of the British
GENERA of aquatic plants belong to the Linnean classes of Mono and
Dioecia; whilst of terrestrial plants (the aquatic genera being
subtracted) only one-thirteenth of the genera belong to these two
classes. Is there any truth in this fact generally? Can aquatic plants,
being confined to a small area or small community of individuals,
require more free crossing, and therefore have separate sexes? But to
return to our point, does not Alph. de Candolle say that aquatic plants
taken as a whole are lowly organised, compared with terrestrial; and may
not Oliver's remark on the separation of the sexes in lowly organised
plants stand in some relation to their being frequently aquatic? Or is
this all rubbish?
... What a magnificent compliment you end your review with! You and
Hooker seem determined to turn my head with conceit and vanity (if not
already turned) and make me an unbearable wretch.
With most cordial thanks, my good and kind friend, Farewell, C. DARWIN.
[The following passage from a letter (July 28, 1863), to Prof.
Hildebrand, contains a reference to the reception of the dimorphic work
in France:--
"I am extremely much pleased to hear that you have been looking at the
manner of fertilisation of your native Orchids, and still more pleased
to hear that you have been experimenting on Linum. I much hope that you
may publish the result of these experiments; because I was told that the
most eminent French botanists of Paris said that my paper on Primula was
the work of imagination, and that the case was so improbable they did
not believe in my results."]
CHARLES DARWIN TO ASA GRAY. April 19 [1864].
... I received a little time ago a paper with a good account of your
Herbarium and Library, and a long time previously your excellent review
of Scott's 'Primulaceae,' and I forwarded it to him in India, as it
would much please him. I was very glad to see in it a new case of
Dimorphism (I forget just now the name of the plant); I shall be
grateful to hear of any other cases, as I still feel an interest in
the subject. I should be very glad to get some seed of your dimorphic
Plantagos; for I cannot banish the suspicion that they must belong to a
very different class like that of the common Thyme. (In this prediction
he was right. See 'Forms of Flowers,' page 307.) How could the
wind, which is the agent of fertilisation, with Plantago, fertilise
"reciprocally dimorphic" flowers like Primula? Theory says this cannot
be, and in such cases of one's own theories I follow Agassiz and
declare, "that nature never lies." I should even be very glad to examine
the two dried forms of Plantago. Indeed, any dried dimorphic plants
would be gratefully received...
Did my Lythrum paper interest you? I crawl on at the rate of two hours
per diem, with 'Variation under Domestication.'
CHARLES DARWIN TO J.D. HOOKER. Down, November 26 [1864].
... You do not know how pleased I am that you have read my Lythrum paper;
I thought you would not have time, and I have for long years looked at
you as my Public, and care more for your opinion than that of all the
rest of the world. I have done nothing which has interested me so much
as Lythrum, since making out the complemental males of Cirripedes.
I fear that I have dragged in too much miscellaneous matter into the
paper.
... I get letters occasionally, which show me that Natural Selection is
making GREAT progress in Germany, and some amongst the young in France.
I have just received a pamphlet from Germany, with the complimentary
title of "Darwinische Arten-Enstehung-Humbug"!
Farewell, my best of old friends, C. DARWIN.
CHARLES DARWIN TO ASA GRAY. September 10, [1867?].
... The only point which I have made out this summer, which could
possibly interest you, is that the common Oxlip found everywhere, more
or less commonly in England, is certainly a hybrid between the primrose
and cowslip; whilst the P. elatior (Jacq.), found only in the
Eastern Counties, is a perfectly distinct and good species; hardly
distinguishable from the common oxlip, except by the length of the
seed-capsule relatively to the calyx. This seems to me rather a horrid
fact for all systematic botanists...
CHARLES DARWIN TO F. HILDEBRAND. Down, November 16, 1868.
My dear Sir,
I wrote my last note in such a hurry from London, that I quite forgot
what I chiefly wished to say, namely to thank you for your excellent
notices in the 'Bot. Zeitung' of my paper on the offspring of dimorphic
plants. The subject is so obscure that I did not expect that any one
would have noticed my paper, and I am accordingly very much pleased
that you should have brought the subject before the many excellent
naturalists of Germany.
Of all the German authors (but they are not many) whose works I have
read, you write by far the clearest style, but whether this is a
compliment to a German writer I do not know.
[The two following letters refer to the small bud-like "Cleistogamic"
flowers found in the violet and many other plants. They do not open and
are necessarily self-fertilised:]
CHARLES DARWIN TO J.D. HOOKER. Down, May 30 [1862].
... What will become of my book on Variation? I am involved in a
multiplicity of experiments. I have been amusing myself by looking at
the small flowers of Viola. If Oliver (Shortly afterwards he wrote:
"Oliver, the omniscient, has sent me a paper in the 'Bot. Zeitung,' with
most accurate description of all that I saw in Viola.") has had time to
study them, he will have seen the curious case (as it seems to me) which
I have just made clearly out, viz. that in these flowers, the FEW pollen
grains are never shed, or never leave the anther-cells, but emit long
pollen tubes, which penetrate the stigma. To-day I got the anther with
the included pollen grain (now empty) at one end, and a bundle of tubes
penetrating the stigmatic tissue at the other end; I got the whole under
a microscope without breaking the tubes; I wonder whether the stigma
pours some fluid into the anther so as to excite the included grains. It
is a rather odd case of correlation, that in the double sweet violet
the small flowers are double; i.e., have a multitude of minute scales
representing the petals. What queer little flowers they are.
Have you had time to read poor dear Henslow's life? it has interested me
for the man's sake, and, what I did not think possible, has even exalted
his character in my estimation...
[The following is an extract from the letter given in part above, and
refers to Dr. Gray's article on the sexual differences of plants:]
CHARLES DARWIN TO ASA GRAY. NOVEMBER 26 [1862].
... You will think that I am in the most unpleasant, contradictory,
fractious humour, when I tell you that I do not like your term of
"precocious fertilisation" for your second class of dimorphism [i.e. for
cleistogamic fertilisation]. If I can trust my memory, the state of
the corolla, of the stigma, and the pollen-grains is different from the
state of the parts in the bud; that they are in a condition of special
modification. But upon my life I am ashamed of myself to differ so much
from my betters on this head. The TEMPORARY theory (This view is now
generally accepted.) which I have formed on this class of dimorphism,
just to guide experiment, is that the PERFECT flowers can only be
perfectly fertilised by insects, and are in this case abundantly
crossed; but that the flowers are not always, especially in early
spring, visited enough by insects, and therefore the little imperfect
self-fertilising flowers are developed to ensure a sufficiency of seed
for present generations. Viola canina is sterile, when not visited by
insects, but when so visited forms plenty of seed. I infer from the
structure of three or four forms of Balsamineae, that these require
insects; at least there is almost as plain adaptation to insects as in
the Orchids. I have Oxalis acetosella ready in pots for experiment
next spring; and I fear this will upset my little theory... Campanula
carpathica, as I found this summer, is absolutely sterile if insects are
excluded. Specularia speculum is fairly fertile when enclosed; and this
seemed to me to be partially effected by the frequent closing of the
flower; the inward angular folds of the corolla corresponding with the
clefts of the open stigma, and in this action pushing pollen from the
outside of the stigma on to its surface. Now can you tell me, does S.
perfoliata close its flower like S. speculum, with angular inward folds?
if so, I am smashed without some fearful "wriggling." Are the IMPERFECT
flowers of your Specularia the early or the later ones? very early or
very late? It is rather pretty to see the importance of the closing of
flowers of S. speculum.
['Forms of Flowers' was published in July; in June, 1877, he wrote to
Professor Carus with regard to the translation:--
"My new book is not a long one, viz. 350 pages, chiefly of the larger
type, with fifteen simple woodcuts. All the proofs are corrected except
the Index, so that it will soon be published.
"... I do not suppose that I shall publish any more books, though perhaps
a few more papers. I cannot endure being idle, but heaven knows whether
I am capable of any more good work."
The review alluded to in the next letter is at page 445 of the volume of
'Nature' for 1878:]
CHARLES DARWIN TO W. THISELTON DYER. Down, April 5, 1878.
My dear Dyer,
I have just read in 'Nature' the review of 'Forms of Flowers,' and I am
sure that it is by you. I wish with all my heart that it deserved one
quarter of the praises which you give it. Some of your remarks have
interested me greatly... Hearty thanks for your generous and most kind
sympathy, which does a man real good, when he is as dog-tired as I am at
this minute with working all day, so good-bye.
C. DARWIN.