To Asa Gray 1 July 1
Down Bromley Kent
My dear Gray
I have been baddish for 2 or 3 weeks, but am better tonight2 & mean to amuse myself (& have no other object) by scribbling a few lines on orchids. Since writing last, I have received your notes on Platanthera Hookeri & on diversity of forms of Cypripedium. On the latter you ought, if you can spare time, to write a paper.3 Platanthera Hookeri is really beautiful & quite a new case. It is almost laughable the viscid discs getting so far apart that the front of the flower has to be divided into two bridal chambers! I have added a note to the German Edition about this & a few words on Cypripedium on your authority.4 On getting your letter I wrote to Trübner to send the dozen copies:5 I wish you would let me pay for them; but you are so punctilious that you would fling without permission first granted the money across the Atlantic in the same shameful manner in which you did the £8.—6
My son George, who is an entomologist, has been watching orchids with enthusiasm & indomitable patience.7 He has made out clearly that it is a Fly, (Empis) which fertilises O. maculata, & probably other Diptera fertilise the closely allied species; it was pretty to see the pollinia affixed to their spherical eyes, & after the act of depression parallel to & rather above the probosces.8 But the most remarkable case is that of Herminium monorchis; he has brought me 24 specimens of very minute Hymenoptera with pollinia attached to all, & always to the same exact spot—viz to the exterior base of femur of front legs. Nothing has given me such an idea of close adaptation of form of whole flower: the labellum hangs obliquely downwards & the minute insects enter between its Edge & the huge viscid disc on one side; & in retreating they hit their prominent femora against the under side of the disc. So closely fitted is the flower to the insect, that my son saw several times insects after entering in a wrong position come out, change their position & reenter.9 So much for orchids: I am fairly astonished at the success of my book (not that I know whether it sells) with Botanists: Berkeley has reviewed it in London R. rather egregiously, & Hooker writes strongly.10 So that now I can dismiss the subject & stick to other work.
Lately I have done very little, except some crossing of plants. I have made a great series of crosses on the peloric flowers of Pelargonium: but I doubt whether I shall get such good results, as I at first hoped with respect to sterility of hybrids.11 By the way Naudin writes that he is going to publish on this subject this autumn: his papers give me the idea that he does not know what has been done in Germany.—12 Rhexia glandulosa, I does require insect agency to set seed; but I see as yet no probability of dimorphism.13 You mentioned some genus (name forgotten without searching your letters) in which you found two forms like Primula, & a third form with both pistil & stamen short.14 Can you tell me whether all flowers on the specimen were thus characterised? I much want to know because Lythrum is trimorphic.—15
Yours ever most sincerely | C. Darwin
Thanks for notes on Cypripedium and Platanthera hookeri, which is really beautiful and quite a new case.
His son, George, has been observing the insect fertilisation of orchids.
CD has been crossing peloric flowers of Pelargonium, but doubts he will get good results with respect to sterility of hybrids.
Rhexia glandulosa does not appear to be dimorphic. Lythrum is trimorphic.