270 BOTANY [CHAP. X 



Letter 600 from flower to flower. By the way, Cephalanthera has single 

 pollen-grains, but this seems to be a case of degradation, for 

 the rostellum is utterly aborted. 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 \DicJi<zd\ has done 

 me one good little turn. I often speculated how the caudicle 

 of Orchis had been formed. 1 I had noticed slight clouds in 

 the substance half way down ; I have now dissected them out, 

 and I find they are pollen-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. 2 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 



1 The gradation here suggested is thoroughly worked out in the 

 Fertilisation of Orchids, Ed. I., p. 323, Ed. II., p. 257. 



2 This view was afterwards given up. 



