312 BOTANY [Chap. X 



Letter 636 of Silliman's N. American Journal) on Gymnadenia tridentata ; 

 namely, to split the labellum of a Cattleya, or of some allied 

 orchis, remove caudicle from pollen-mass (so that no loose 

 grains are about) and put it carefully into the large tongue- 

 like rostellum, and see if pollen-tubes will penetrate, or better, 

 see if capsule will swell. Similar pollen-masses ought to be put 

 on true stigmas of two or three other flowers of same plants 

 for comparison. It is to discover whether rostellum yet 

 retains some of its primordial function of being penetrated by 

 pollen-tubes. You will be sorry that you ever entered into 

 correspondence with me. But do not answer till at leisure, 

 and as briefly as you like. My handwriting, I know, is dread- 

 fully bad. Excuse this scribbling paper, as I can write faster 

 on it, and I have a rather large correspondence to keep up. 



Letter 637 To J. Scott. 



Down, Jan. 21st, 1863. 



I thank you for your very interesting letter ; I must 

 answer as briefly as I can, for I have a heap of other letters 

 to answer. I strongly advise you to follow up and publish 

 your observations on the pollen-tubes of orchids ; they promise 

 to be very interesting. If you could prove what I only con- 

 jectured (from state of utriculi in rostellum and in stigma of 

 Catasetum and Acroperd) that the utriculi somehow induce, 

 or are correlated with, penetration of pollen-tubes you will 

 make an important physiological discovery. I will mention, 

 as worth your attention (and what I have anxiously wished 

 to observe, if time had permitted, and still hope to do) — viz., 

 the state of tissues or cells of stigma in an utterly sterile 

 hybrid, in comparison with the same in fertile parent species ; 

 to test these cells, immerse stigmas for 48 hours in spirits of 

 wine. I should expect in hybrids that the cells would not 

 show coagulated contents. It would be an interesting dis- 

 covery to show difference in female organs of hybrids and 

 pure species. Anyhow, it is worth trial, and I recommend 

 you to make it, and publish if you do. The pollen-tubes 

 directing themselves to stigma is also very curious, though 

 not quite so new, but well worth investigation when you 

 get Cattleya, etc., in flower. I say not so new, for remember 

 small flowers of Viola and Oxalis ; or better, see Biblio- 

 graphy in Natural History Review, No. VIII., page 419 



