446 THE UNFINISHED BOOK. [1857, 



C. Darwin to J. D. Hooker. 



* Dec. 24th [1856]. 



. > . How I do wish I lived near you to discuss matters 

 with. I have just been comparing- definitions of species, and 

 stating briefly how systematic naturalists work out their sub- 

 jects. Aquilegia in the Flora Indica was a capital example 

 for me. It is really laughable to see what different ideas are 

 prominent in various naturalists' minds, when they speak of 

 *' species ; " in some, resemblance is everything and descent 

 of little weight in some, resemblance seems to go for noth- 

 ing, and Creation the reigning idea in some, descent is the 

 key, in some, sterility an unfailing test, with others it is not 

 worth a farthing. It all comes, I believe, from trying to de- 

 fine the undefinable. I suppose you have lost the odd black 

 seed from the birds' dung, which germinated, anyhow, it is 

 not worth taking trouble over. I have now got about a dozen 

 seeds out of small birds' dung. Adios, 



My dear Hooker, ever yours, 



C. DARWIN. 



C. Darwin to Asa Gray. 



Down, Jan. 1st [1857?]. 



MY DEAR DR GRAY, I have received the second part of 

 your paper,* and though I have nothing particular to say, I 

 must send you my thanks and hearty admiration. The whole 

 paper strikes me as quite exhausting the subject, and I quite 

 fancy and flatter myself I now appreciate the character of 

 your Flora. What a difference in regard to Europe your re- 

 mark in relation to the genera makes ! I have been eminently 

 glad to see your conclusion in regard to the species of large 

 genera widely ranging; it is in strict conformity with the re- 

 sults I have worked out in several ways. It is of great impor- 

 tance to my notions. By the way you have paid me a great 



* Statistics of the Flora of the Northern U. States.' Sillimans Jour- 

 nal, 1857 



