- 
J. C. Draper—Evolution of Structure in Seedlings. 898 
of carbonic acid by the roots, and its exhalation by the leaves 
when light is no longer present. 
e change, on the contrary, appears to arise out of the fact 
that two essentially different operations have been confounded, 
viz: the actual growth or evolution of structures in the plant, 
and the decomposition of carbonic acid by the leaves under the 
influence of the light, to provide the gum or other materials 
that are to be organized. These two factors are separated by 
Prof. J. W. Draper in his disscusion of the conditions of growth 
ia plants. We propose to show that by adopting this proposi- 
on of two distinct operations in the higher plants, all the 
apparent discrepancies regarding the growth of these plants are 
explained. 
The growth of seedlings in the dark offering conditions in 
which the act of growth or evolution of structure is accom- 
ott without the collateral decomposition of carbonic acid, 
arranged two series of experiments in which growth under 
this condition might be studied and compared with a similar 
growth in the light. That the experiments might continue over 
® sufficient period of time to furnish reliable comparative results, 
_Iselected peas as the subject of trial, since these seeds contain 
Sufficient material to support the growth of seedlings for a 
couple of weeks. 
or germination, viz., darkness, was secured ; the second, warmth, 
rl inders 
Shenae for each and keeping the level of the water the same in 
th. 
Since the upper part of each tube presented a similar opening 
70° to 80° F., while regularity and uniformity in the ~ 
this the growth of the seedling was marked every twelve hours. 
Am. Joun. Sc1.—Turp Sertes, Vou. IV, No. 23.—Nov., 1872. . 
25 
