To J. D. Hooker [28 July – 10 August 1861]1
2. Hesketh Crescent | Torquay
Read this if ever you have time & inclination—
My dear Hooker
Many thanks for names & all information & for your enquiring about Epithecia.2 Veitch sent me a grand lot this morning.3 What wonderful structures! I have now seen enough, & you must not send me more, for though I enjoy looking at them much, & 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.4 I suppose it cannot be one of the stigmas: 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 M.S. folio pages!!!5 The beauty of the adaptations of parts seems to me unparalleled. I shd. think or guess waxy pollen was most differentiated. In Cypripedium which seems least modified & a much exterminated group, the grains are single.6 In all others as far as I have seen they are in packets of 4; & these packets cohere into many wedge-formed masses in Orchis; into 8, 4 & finally two. It seems curious that a flower shd. exist which could at most fertilise only 2 other flowers, seeing how abundant pollen generally is: this fact I look at as explaining the perfection of the contrivances by which the pollen, so important from its fewness, is carried from flower to flower. By the way Cephalanthera has single pollen-grains; but this seems to be a case of degradation for rostellum is utterly aborted.7 Oddly the columns of pollen are here kept in place by very early penetration of pollen-tubes into the edge of the stigma: nevertheless it receives more pollen by insect agency.—
Epithecia has done me one good little turn: I often speculated how the caudicle of Orchis had been formed. I had noticed slight clouds in its substance half way down: I have now dissected them out, & I find they are pollen-grains fairly embedded & useless. If you suppose the pollen-grain to abort in the lower half of the pollinia of Epipactis; but the parallel elastic threads to remain & cohere; you have the caudicle of Orchis & can understand the few embedded & functionless pollen-grains.—8
I must not look at any more exotic orchids; hearty thanks for your offer. But if you would make one single observation for me on Cypripedium, I should be glad. Asa Gray writes to me that the outside of pollen-masses is sticky in this genus:9 I find that the whole mass consists of pollen-grain immersed in a sticky brownish thick fluid. You could tell by a mere lens & pen-knife.— If it is, as I found it, pollen could not get on stigma without insect-aid.—10 Cypripedium confounds me much: I conjecture that drops of nectar are secreted by surface of Labellum beneath the anthers & in front of stigma, & that the shield over the anthers & form of Labellum is to compel insects to insert their probosces all round both organs.11 It would be troublesome for you to look to this; as it is always bothersome to catch the nectar secreting; & the cup of Labellum gets filled with water by gardeners watering.—
I have examined Listera, ovata, cordata & nidus avis; the pollen is uniform: I suspect you must have seen some observation founded on mistake from the penetration & hardening of sticky fluid from rostellum, which does penetrate the pollen a little.—12
It is mere virtue which makes me not wish to examine more orchids; for I like it far better than writing about varieties of cocks & Hens & Ducks.—13 Nevertheless I have just been looking at Lindleys list in Veg. K. & I cannot resist one or two of his great Division of Arethuseæ, which includes Vanilla.14 And as I know so well the Ophreæ, I shd like (God forgive me) any one of the Satyriadæ, Disidæ, & Corycidæ.—
I fear my long lucubration will have wearied you; but it has amused me to write, so forgive me.— Ever your affect | C. Darwin
I am very sorry that I have failed to see Catasetum & Mormodes; I think I could have madout all & means of ejection of pollinia. Let me know affinities of Epithecia. I marvel often as I think over the diversity & perfection of the contrivances.—
There is a Dutch(!) Translation of “Origin” come out.—15
Puzzled by function of orchids’ rostellum.
Orchids’ pollen concentrated in two pollinia; hence one flower can fertilise only two others. This may explain precision of orchid pollination mechanisms.