RESPIRATION. 109 
the influence of light. The parts not coloured green, such as the 
wall fruit, seeds, red and yellow leaves, &c., always respire in one 
and the same manner: whether exposed to light or left in dark- 
ness, they always absorb the oxygen and disengage carbonic acid. 
They respire in the same manner as animals. If we consider that 
the green parts of the plant are far more numerous than those 
which are otherwise coloured,—that the clear light nights of hot 
countries may rather be said to diminish than to interrupt their 
respiration,—that the season of long days in northern countries is 
that of the greatest vegetative activity—we shall be led to the con- 
clusion that the great mass of plants live more in light than in 
darkness, and consequently that their diurnal respiration greatly 
preponderates over their nocturnal. e diurnal respiration of 
plants, which pours into the air considerable quantities of oxygen 
gas, happily compensates for the effects of animal respiration, 
which produces carbonic acid gas, injurious to the life of man. 
Plants purify the air injured by the respiration of men and 
animals. If animals transform the oxygen of the air into carbonic 
acid, plants take this carbonic acid back again by their diurnal 
respiration. They fix the carbon in the depth of their tissues, and 
return oxygen to the air, in reparation. 
Such is the admirable equilibrium which the Creator has estab- 
lished between animals and plants, such the beneficial communica- 
tion which assures to the air its constant soundness, and maintains 
it in that state of purity which is indispensable to support the life 
of the living creatures which cover the globe. 
We have now been speaking of the respiration of aerial plants. 
Water plants cannot respire by the same organic mechanism. In 
these the air circulating across the intercellular meatus of the 
leaves acts directly upon the pithy contents of the’ cells. The 
leaves of aquatic plants, which are destitute of epidermis, and are 
in general very slight, borrow air which the water holds in solution, 
m such a manner that, according to the ingenious remark of 
M. Brongniart, they respire in a manner analogous to that pre- | 
sented by fishes and other animals which breathe by gills. 
Plants which live in perpetual darkness, and which consequently 
are always subject to nocturnal respiration, maintain certain modi- 
fications in: their exterior aspect. In this anomalous condition 
