98 The American Naturalist. [February, 
THE GASES IN LIVING PLANTS. 
(Continued from Vol. XXVII, page 7.) 
By J. C. ARTHUR. 
Kinps oF GASES AND RELATIVE AMOUNTS. 
It is.now our duty to give a brief statement of the kinds, ` 
the source and the movements of gases in plants. E 
Plants are permeated by the same gases that make up the | 
atmosphere surrounding them: oxygen, carbon dioxide and 
nitrogen. Nitrogen in the form of a gas is neither used nor 
generated by any part of plants, unless we except the tuber- 
cles of certain roots, and so it occurs in about the same per- — 
centage inside the plant as outside of it. On the other hand, 
both oxygen and carbon dioxide enter into combination with, 
and. are liberated from, the plant tissues in varying amounts 
at different times. The percentage of these two gases in the — 
cavities of the plant vary through a considerable range. Ina 
series of determinations made by Lawes, Gilbert and Pugh, in ~ 
England, the oxygen ranged from 3 to 10 per cent., and the — 
_ carbon dioxide from 14 to 21 per cent in plants which had — 
been for some time in the dark, while plants which had been © 
standing in sunlight reversed these figures, and gave 24 to 27 _ 
per cent. of oxygen and 3 to 6 per cent. of carbon dioxide. 
The two gases, therefore, bear a somewhat reciprocal relation, 
their sum usually being about 25 to 30 per cent. of the total — 
gas in the plant. K 
a a eee a, ee et eee Spe 
VARIATION IN AMOUNT DUE TO ASSIMILATION. 
