20 GEOGRAPHICAL DISTRIBUTION [Chap. VII 



Letter 393 make some generalisations wherever possible, as I am not 

 at all afraid of having to alter my views in many points of 

 detail. I was so overwhelmed with zoological details, that 

 I never went through the Geological Society's Journal as I 

 ought to have done, and as I mean to do before writing more 

 on the subject. 



Letter 394 To F. Buchanan White. 1 



Down, Sept. 23rd [1878]. 

 I have now read your paper, and I hope that you will not 

 think me presumptuous in writing another line to say how 

 excellent it seems to me. I believe that you have largely 

 solved the problem of the affinities of the inhabitants of this 

 most interesting little island, and this is a delightful triumph. 



Letter 395 To J. D. Hooker. 



Down, July 22nd [1879]. 

 I have just read Ball's Essay. 2 It is pretty bold. The 

 rapid development as far as we can judge of all the higher 

 plants within recent geological times is an abominable 



1 " Written in acknowledgment of a copy of a paper (published by me 

 in the Proceedings of the Zoolog. Soc.) on the Hemiptera of St. Helena, 

 but discussing the origin of the whole fauna and flora of that island." — 

 F. B. W. 



s The late John Ball's lecture " On the Origin of the Flora of the 

 Alps" in the Proceedings of the R. Geogr. Soc, 1879. Ball argues (p. 18) 

 that " during ancient Palaeozoic times, before the deposition of the Coal- 

 measures, the atmosphere contained twenty times as much carbonic acid 

 gas and considerably less oxygen than it does at present." He further 

 assumes that in such an atmosphere the percentage of CO. in the higher 

 mountains would be excessively different from that at the sea-level, 

 and appends the result of calculations which gives the amount of C0 2 

 at the sea-level as 100 per 10,000 by weight, at a height of 10,000 feet 

 as I2"5 per 10,000. Darwin understands him to mean that the Vascular 

 Cryptogams and Gymnosperms could stand the sea-level atmosphere, 

 whereas the Angiosperms would only be able to exist in the higher 

 regions where the percentage of C0 2 was small. It is not clear to us that 

 Ball relies so largely on the condition of the atmosphere as regards C0 2 . 

 If he does he is clearly in error, for everything we know of assimilation 

 points to the conclusion that 100 per 10,000 (1 per cent.) is by no 

 means a hurtful amount of CO.,, and that it would lead to an especially 

 vigorous assimilation. Mountain plants would be more likely to descend 

 to the plains to share in the rich feast than ascend to higher regions to 



