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 cla.s.s 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 Aga.s.siz 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 t.i.tle 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 mult.i.tude 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 s.e.xual 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 cla.s.s 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 cla.s.s 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.
CHAPTER 2.XIII. -- CLIMBING AND INSECTIVOROUS PLANTS.
[My father mentions in his "Autobiography" (volume i.) that he was led to take up the subject of climbing plants by reading Dr. Gray"s paper, "Note on the Coiling of the Tendrils of Plants." ("Proc. Amer. Acad. of Arts and Sciences," 1858.) This essay seems to have been read in 1862, but I am only able to guess at the date of the letter in which he asks for a reference to it, so that the precise date of his beginning this work cannot be determined.
In June 1863 he was certainly at work, and wrote to Sir J.D. Hooker for information as to previous publications on the subject, being then in ignorance of Palm"s and H. v. Mohl"s works on climbing plants, both of which were published in 1827.]
CHARLES DARWIN TO J.D. HOOKER. Down [June] 25 [1863].
My dear Hooker,
I have been observing pretty carefully a little fact which has surprised me; and I want to know from you and Oliver whether it seems new or odd to you, so just tell me whenever you write; it is a very trifling fact, so do not answer on purpose.
I have got a plant of Echinocystis lobata to observe the irritability of the tendrils described by Asa Gray, and which of course, is plain enough. Having the plant in my study, I have been surprised to find that the uppermost part of each branch (i.e. the stem between the two uppermost leaves excluding the growing tip) is CONSTANTLY and slowly twisting round making a circle in from one-half to two hours; it will sometimes go round two or three times, and then at the same rate untwists and twists in opposite directions. It generally rests half an hour before it retrogrades. The stem does not become permanently twisted. The stem beneath the twisting portion does not move in the least, though not tied. The movement goes on all day and all early night. It has no relation to light for the plant stands in my window and twists from the light just as quickly as towards it. This may be a common phenomenon for what I know, but it confounded me quite, when I began to observe the irritability of the tendrils. I do not say it is the final cause, but the result is pretty, for the plant every one and a half or two hours sweeps a circle (according to the length of the bending shoot and the length of the tendril) of from one foot to twenty inches in diameter, and immediately that the tendril touches any object its sensitiveness causes it immediately to seize it; a clever gardener, my neighbour, who saw the plant on my table last night, said: "I believe, Sir, the tendrils can see, for wherever I put a plant it finds out any stick near enough." I believe the above is the explanation, viz.
that it sweeps slowly round and round. The tendrils have some sense, for they do not grasp each other when young.
Yours affectionately, C. DARWIN.
CHARLES DARWIN TO J.D. HOOKER. Down, July 14 [1863].
My dear Hooker,
I am getting very much amused by my tendrils, it is just the sort of niggling work which suits me, and takes up no time and rather rests me whilst writing. So will you just think whether you know any plant, which you could give or lend me, or I could buy, with tendrils, remarkable in any way for development, for odd or peculiar structure, or even for an odd place in natural arrangement. I have seen or can see Cucurbitaceae, Pa.s.sion-flower, Virginian-creeper, Cissus discolor, Common-pea and Everlasting-pea. It is really curious the diversification of irritability (I do not mean the spontaneous movement, about which I wrote before and correctly, as further observation shows): for instance, I find a slight pinch between the thumb and finger at the end of the tendril of the Cucurbitaceae causes prompt movement, but a pinch excites no movement in Cissus. The cause is that one side alone (the concave) is irritable in the former; whereas both sides are irritable in Cissus, so if you excite at the same time both OPPOSITE sides there is no movement, but by touching with a pencil the two branches of the tendril, in any part whatever, you cause movement towards that point; so that I can mould, by a mere touch, the two branches into any shape I like...