430 GEOGRAPHICAL DISTRIBUTION [CHAP. VI 



Letter 328 One more favour. Do not, I pray you, speak of your 

 letters troubling me. I should be sorry indeed to have you 

 stop, or write more rarely, even though mortified to find that 

 I can so seldom give you the information you might reason- 

 ably expect. 



Letter 329 To Asa Gray. 



Down, August 24th [1856]. 



I am much obliged for your letter, which has been very 

 interesting to me. Your " indefinite " answers are perhaps 

 not the least valuable part ; for Botany has been followed in 

 so much more a philosophical spirit than Zoology, that I 

 scarcely ever like to trust any general remark in Zoology 

 without I find that botanists concur. Thus, with respect to 

 intermediate varieties being rare, I found it put, as I suspected, 

 much too strongly (without the limitations and doubts which 

 you point out) by a very good naturalist, Mr. Wollaston, in 

 regard to insects ; and if it could be established as true it 

 would, I think, be a curious point. Your answer in regard to 

 the introduced plants not being particularly variable, agrees 

 with an answer which Mr. H. C. Watson has sent me in 

 regard to British agrarian plants, or such (whether or no 

 naturalised) [as] are now found only in cultivated land. It 

 seems to me very odd, without any theoretical notions of 

 any kind, that such plants should not be variable ; but the 

 evidence seems against it. 



Very sincere thanks for your kind invitation to the United 

 States : in truth there is nothing which I should enjoy more ; 

 but my health is not, and will, I suppose, never be strong 

 enough, except for the quietest routine life in the country. 

 I shall be particularly glad of the sheets of your paper on 

 geographical distribution ; but it really is unlikely in the 

 highest degree'that I could make any suggestions. 



With respect to my remark that I supposed that there 

 were but few plants common to Europe and the United States, 

 not ranging to the Arctic regions ; it was founded on vague 

 grounds, and partly on range of animals. But I took 

 H. C. Watson's remarks (1835) and in the table at the end I 

 found that out of 499 plants believed to be common to the 

 Old and New World, only 1 10 did not range on either side of 

 the Atlantic up to the Arctic region. And on writing to 



