272 BOTANY [CHAP. X 



Letter 601 besides the white and yellow varieties of the same species. 

 It will be tiresome work, but if I can anyhow get the plants, 

 it shall be tried. 



Thirdly : Can you give me seeds of any Rubiaceae of the 

 sub-order Cinchoneae, as Spermacoce, Diodia, Mitchella, Olden- 

 landia ? Asa Gray says they present two forms like Primula. 

 I am sure that this subject is well worth working out. I have 

 just almost proved a very curious case in Linum grandiflorum 

 which presents two forms, A and B. Pollen of A is per- 

 fectly fertile on stigma of A. But pollen of B is absolutely 

 barren on its own stigma ; you might as well put so much 

 flour on it. It astounded me to see the stigmas of B purple 

 with its own pollen ; and then put a few grains of similar- 

 looking pollen of A on them, and the germen immediately 

 and always swelled ; those not thus treated never swelling. 



Fourthly : Can you give me any very hairy Saxifraga (for 

 their functions) [i.e. the functions of the hairs] ? 



I send you a resume of my requests, to save you trouble. 

 Nor would I ask for so much aid if I did not think all these 

 points well worth trying to investigate. 



My dear old friend, a letter from you always does me a 

 world of good. And, the Lord have mercy on me, what a 

 return I make. 



Letter 602 To J. D. Hooker. 



Down, Oct. 4th [1861]. 



Will you have the kindness to read the enclosed, and look 

 at the diagram. Six words will answer my question. It is 

 not an important point, but there is to me an irresistible 

 charm in trying to make out homologies. 1 You know the 

 membranous cup or clinandrum, in many orchids, behind the 

 stigma and rostellum : it is formed of a membrane which unites 

 the filament of the normal dorsal anther with the edges of 

 the pistil. The clinandrum is largely developed in Malaxis^ 

 and is of considerable importance in retaining the pollinia, 

 which as soon as the flower opens are quite loose. 



The appearance and similarity of the tissues, etc., at once 



1 In 1880 he wrote to Mr. Bentham : " It was very kind of you to 

 write to me about the Orchideae, for it has pleased me to an extreme 

 degree that I could have been of the least use to you about the nature of 

 the parts." Life and Letters, III., p. 264. 



