Ill 
rect influence of the sun ; so that the decomposition 
of carbonic acid, and the formation of the green 
colour, not only occur at the same time, and in the 
same place, but they are accomplished by the imme- 
diate operation of the same powerful agent. There 
exists, says M. Senebier, a very singular relation be- 
tween the parts of leaves which furnish most air, and 
those of etiolated leaves which first become green. 
It is in the angles formed by the nerves of the leaves 
that we observe these two phenomena. It is in these 
that the excretory vessels of the parenchyme termi- 
nate, and it is there that light announces its operation, 
as we see by the air which this part affords, and by 
the green colour which at the same time it assumes *. 
353. But not only do these operations appear thus 
to go on at the same time, and in the same part of 
the plant, but they seem to have a near connec- 
tion with each other ; for it is only by the green 
parts of vegetables that oxygen gas is afforded j 
while all their other parts yield only an impure air. 
M. Senebier made many experiments on the seminal 
leaves of French beans, and on the young leaves of 
other plants, but never obtained from them any oxygen 
gas while they retained their white colour. Neither 
did the etiolated leaves of lettuce or cabbage afford 
air when exposed to the sun, or the little which they 
sometimes yielded, was always very impure f- Why, 
then, should the decomposition of carbonic acid al- 
ways attend the production of the green colour in 
plants, and why should their white colour appeaj 
-* Mem. Phys. Chim. t. ii. p. 98. t Ibid. t. i. p. HO. 
