ABSORPTION OF MOISTURE BY TREES. 
167 
extract from the air a much larger supply. The obvious con¬ 
clusion as to the source from which the extraordinary quantity 
of sap at this season is derived, is that to which scientific 
investigation leads us, namely, that it is absorbed from the 
earth by the roots, and thence distributed to all parts of the 
plant. Popular opinion, indeed, supposes that all the vege¬ 
table fluids, during the entire period 0 f growth, are thus 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, not only is the solid matter of the tree, in 
a certain proportion not important to our present inquiry, 
received from the atmosphere in a gaseous form, through the 
pores of the leaves and of the young shoots, but water in the 
state of vapor is absorbed and contributed to the circulation, 
by the same organs.* The amount of water taken up by the 
roots, however, is vastly greater than that imbibed through the 
leaves, especially at the season when the juices are most abun- 
* “ The presence of watery vapor in the air is general. * * * Vege¬ 
table surfaces are endowed with the power of absorbing gases, vapors, 
and also, no doubt, the various soluble bodies which are presented to them. 
The inhalation of humidity is carried on by the leaves upon a large scale; 
the dew of a cold summer night revives the groves and the meadows, and 
a single shower of rain suffices to refresh the verdure of a forest which a 
long drought had parched.”— SonAOHT, Les Arbres , ix, p. 340. 
The absorption of the vapor of water by leaves is disputed. “ The 
absorption of watery vapor by the leaves of plants is, according to Unger’s 
experiments, inadmissible.”— Wilhelm, Der Boden und das Wdsser, p. 19. 
If this latter view is correct, the apparently refreshing effects of atmos¬ 
pheric humidity upon vegetation must be ascribed to moisture absorbed by 
the ground from the air and supplied to the roots. In some recent experi¬ 
ments by Dr. Sachs, a porous flower-pot, with a plant growing in it, was 
left unwatered until the earth was dry, and the plant began to languish. 
The pot was then placed in a glass case containing air, which was kept 
always saturated with humidity, but no water was supplied, and the leaves 
of the plant were exposed to the open atmosphere. The soil in the flower 
pot absorbed from the air moisture enough to revive the foliage, and keep 
it a long time green, but not enough to promote development of new leaves. 
—Id., ibid., p. 18. 
