-grains fairly
embedded and useless. If you suppose the pollen-grains to abort in
the lower half of the pollinia of Epipactis, but the parallel elastic
threads to remain and cohere, you have the caudicle of Orchis, and can
understand the few embedded and functionless pollen-grains. 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 the pollen-masses
is sticky in this genus; I find that the whole mass consists of
pollen-grains immersed in a sticky brownish thick fluid. You could tell
by a mere lens and penknife. If it is, as I find it, pollen could not
get on the stigma without insect aid. Cypripedium confounds me much.
I conjecture that drops of nectar are secreted by the surface of the
labellum beneath the anthers and in front of the stigma, and that the
shield over the anthers and the form of labellum is to compel insects
to insert their proboscis all round both organs. (600/3. This view was
afterwards given up.) It would be troublesome for you to look at this,
as it is always bothersome to catch the nectar secreting, and the cup of
the labellum gets filled with water by gardener's watering.

I have examined Listera ovata, cordata, and Neottia nidus avis: the
pollen is uniform; I suspect you must have seen some observation founded
on a mistake from the penetration and hardening of sticky fluid from the
rostellum, which does penetrate the pollen a little.

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 and hens and
ducks. Nevertheless, I have just been looking at Lindley's list in
the "Vegetable Kingdom," and I cannot resist one or two of his great
division of Arethuseae, which includes Vanilla. And as I know so well
the Ophreae, I should like (God forgive me) any one of the Satyriadae,
Disidae and Corycidae.

I fear my long lucubrations will have wearied you, but it has amused me
to write, so forgive me.

LETTER 601. TO J.D. HOOKER.

(601/1. Part of the following letter is published in the "Life and
Letters," the remainder, with the omission of part bearing on the
Glen Roy problem, is now given as an example of the varied botanical
assistance Darwin received from Sir Joseph Hooker. For the part relating
to Verbascum see the "Variation of Animals and Plants," Edition II.,
1875, Vol