verwhelmed 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.

(394/1. "Written in acknowledgment of a copy of a paper (published by me
in the "Proceedings of the Zoological Society") on the Hemiptera of St.
Helena, but discussing the origin of the whole fauna and flora of that
island."--F.B.W.)

Down, September 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. (395/1. 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 (page 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 CO2 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 CO2 at the sea-level as 100
per 10,000 by weight, at a height of 10,000 feet as 12.5 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 CO2 was small. It is not clear to us that Ball relies so
largely on the condition of the atmosphere as regards CO2. 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 CO2, 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 avoid
it. Ball draws attention to the imperfection of our plant records as
regards the floras of mountain regions. It is, he thinks, conceivable
that there existed a vegetation on the Carboniferous mountains of which
no traces have bee