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.