J. LeConte on the Correlation of Forces. 313 
the roots, the decomposition of this CO, by means of light 
with the fixation of the carbon and the elimination of the oxy- 
gen: 2nd, the recomposition and evolution of Co,. The decom- 
position of CO, undoubtedly takes place in the leaves, but where 
the recomposition of CO, takes place is not so well ascertained. 
It is exhaled however, like the oxygen, from the leavés. The 
process of decomposition of CO, takes place only during the day 
as light is absolutely necessary for this process. The recompost- 
tion of CO, takes place night and day, although its exhalation 
according to some observers seems to be more abundant during 
the night. The process of decomposition of CO, is well under- 
stood—of that of recomposition our knowledge is very imperfect. 
M. Risler’s explanation of this latter process seems most probable. 
Plants, we have seen, undoubtedly absorb soluble organic mat- 
ter, i.¢., humus. Humus we know is a more highly carbonized 
substance than cellulose or starch. This humus is therefore 
oxydized in the roots and interior of the trunk, away from light, 
by means of oxygen also absorbed by the roots and thus forms 
2 
composed in the leaves during the day, then of | 
difference between the amount exhaled during the night and day 
Would enter as an element in the calculation. Also it would 
seem that those plants, especially, which frequent rich shady 
less oxygen, 
até combined in various proportions. The Ist must of course 
be considered = is ns 2 at and necessary, the 2nd being 
OV., 1859. 
