appear.

[Footnote 1: See Lectures on the Physiology of Plants. By Sidney Howard
Vines, Cambridge, England. University Press, 1886. Page 92.]

This constant escape of water from the leaves causes a current to flow
from the roots through the stem into the cells of the leaves. The dilute
mineral solutions absorbed by the roots[1] are thus brought where they
are in contact with the external air, concentrated by the evaporation of
water, and converted in these cells into food materials, such as starch.
The presence of certain mineral matters, as potassium, iron, etc., are
necessary to this assimilating process, but the reason of their necessity
is imperfectly understood, as they do not enter in the products formed.

[Footnote 1: See page 48.]

The amount of water exhaled is often very great. Certain plants are used
for this reason for the drainage of wet and marshy places. The most
important of these is the Eucalyptus tree.[1]

[Footnote 1: Reader in Botany. XII. Transpiration.]

"The amount of water taken from the soil by the trees of a forest and
passed into the air by transpiration is not so large as that accumulated
in the soil by the diminished evaporation under the branches. Hence, there
is an accumulation of water in the shade of forests which is released
slowly by drainage.[1] But if the trees are so scattered as not materially
to reduce evaporation from the ground, the effect of transpiration in
diminishing the moisture of the soil is readily shown. It is noted,
especially in case of large plants having a great extent of exhaling