S8 THE UNFINISHED BOOK. [1856. 



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 

 subjects. 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 

 nothing, 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 

 define 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 

 remark 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 



* ' Statistics of the Flora of the Northern United States.' Sillimaii's 

 Journal, 1857. 



