168 
MOSSES AND FUNGI. 
dant, and when, as we have seen, the leaves are yet in embryo. 
The quantity of water thus received from the air and the earth, 
in a single year, by a wood of even a hundred acres is very 
great, though experiments are wanting to furnish the data for 
even an approximate estimate of its measure; for only the 
vaguest conclusions can be drawn from the observations which 
have been made on the imbibition and exhalation of water by 
trees and other plants reared in artificial conditions diverse 
from those of the natural forest.* 
Wood Mosses and Fungi . 
Besides the water drawn by the roots from the earth, and 
the vapor absorbed by the leaves from the air, the wood 
mosses and fungi, which abound in all dense forests, take up 
a great quantity of moisture from the atmosphere when it is 
charged with humidity, and exhale it again when the air is 
dry. These humble organizations, which play a more import¬ 
ant part in regulating the humidity of the air than writers on 
the forest have usually assigned to them, perish with the trees 
they grow on ; but, in many situations, nature provides a com¬ 
pensation for the tree mosses in ground species, which, on cold 
soils, especially those with a northern exposure, spring up 
abundantly both before the woods are felled, and when the 
land is cleared and employed for pasturage, or deserted. 
These mosses discharge a portion of the functions appropriated 
to the wood, and while they render the soil of improved lands 
much less fit for agricultural use, they, at the same time, pre¬ 
pare it for the growth of a new harvest of trees, when the 
infertility they produce shall have driven man to abandon it 
and suffer it to relapse into the hands of nature.f 
* The experiments of Hales and others, on the absorption and exhala¬ 
tion of water by vegetables, are of the highest physiological interest; but 
observations on sunflowers, cabbages, hops, and single branches of isolated 
trees, growing in artificially prepared soils and under artificial conditions, 
furnish no trustworthy data for computing the quantity of water received 
and given off by the natural wood. 
+ In the primitive forest, except where the soil is too wet for the dense 
