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