PLANTS. 
ted in the greatest quantity when the plants are ex- 
posed to the bright light of day. The sun’s influ- 
ence appears to assist them powerfully in this pro- 
cess, and light is so essentially necessary that no 
respirable air is passed off from their leaves in its 
absence. 
The air which is absorbed from the atmosphere 
by plants, is of the same nature as that which floats 
on all fermenting surfaces ; it is well known in the 
brewery, and gives spirit to the mineral waters: — this 
used to be called fixed air, but is now named car- 
bonic acid gas. 
The leaves of plants are known to imbibe water as 
well as air; and this accounts for the great effect which 
dew, slight showers, and even wetting the leaves, 
have in recruiting the strength of the plants. M. 
Bonnet has proved, that leaves continue to live for 
weeks when one of their surfaces is applied to water, 
and that they not only vegetate themselves, but 
even imbibe enough to support the vegetation of a 
whole branch, and the leaves belonging to it. He 
discovered also, that the two surfaces of leaves differ 
very considerably in their absorbing power; that in 
trees and shrubs, the absorbing property is almost 
confined to the under surface, while the contrary 
holds in many other plants. 
That all vegetables owe their green colour to the 
action of light, is sufficiently obvious, since a plant 
confined in a dark place will consequently be white; 
in this situation its natural propensity will not leave 
it, it will seek that which is intended to promote 
