THE FOREST AS ORGANIC. 183 
trary result, and it is now generally held that no water is taken 
in by the pores of vegetables. Late observations by Cailletet 
in France, howeyer, tend to the establishment of a new doctrine 
on this subject which solves many difficulties and will probably 
be accepted by botanists as definitive. Cailletet finds that 
under normal conditions, that is, when the soil is humid enough 
to supply sufficient moisture through the roots, no water is 
absorbed by the leaves, buds, or bark of plants, but when the 
roots are unable to draw from the earth the requisite quantity 
of this fluid, the vegetable pores in contact with the atmosphere 
absorb it from that source. 
Popular opinion, indeed, supposes that all the vegetable fluids, 
during the entire period of growth, are drawn from the bosom 
of the earth, and that the wood and other products of the tree 
are wholly formed from matter held in solution in the water 
abstracted by the roots from the ground. This is an error, for 
the solid matter of the tree, in a certain proportion nct impor- 
tant to our present inquiry, is received from the atmosphere in 
a gaseous form, through the pores of the leaves and of the 
young shoots, and, as we have just seen, moisture is sometimes 
supplied to trees by the atmosphere. The amount of water 
taken up by the roots, however, is vastly greater than that im- 
bibed through the leaves and bark, especially at the season 
when the sap is most abundant, and when the leaves are yet in 
embryo. The quantity of water thus received from the air and 
the earth, ina single year, even by a wood of only 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.* 
vegetables are of high 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 « ata for 
computing the quantity of water received and given off by the natural wood. 
