o 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
surface, such, for instance, as the common sunflower. Among the plants
which have been successfully employed in the drainage of marshy soil by
transpiration probably the species of Eucalyptus (notably _E_. _globulus_)
are most efficient."[2]

[Footnote 1: Reader in Botany. XIII. Uses of the Forests.]

[Footnote 2: Physiological Botany, page 283.]

4. _Assimilation_.--It is not easy to find practical experiments on
assimilation. Those which follow are taken from "Physiological Botany" (p.
305).

Fill a five-inch test tube, provided with a foot, with fresh drinking
water. In this place a sprig of one of the following water
plants,--_Elodea Canadensis, Myriophyllum spicatum, M.
verticillatum_, or any leafy _Myriophyllum_ (in fact, any small-
leaved water plant with rather crowded foliage). This sprig should be
prepared as follows: Cut the stem squarely off, four inches or so
from the tip, dry the cut surface quickly with blotting paper, then
cover the end of the stein with a quickly drying varnish, for
instance, asphalt-varnish, and let it dry perfectly, keeping the rest
of the stem, if possible, moist by means of a wet cloth. When the
varnish is dry, puncture it with a needle, and immerse the stem in
the water in the test tube, keeping the varnished larger end
uppermost. If the submerged plant be now exposed to the strong rays
of the sun, bubbles of oxygen gas will begin to pass off at a rapid
and even rate, but not too fast to be easily counted. If the simple
apparatus has begun to give off a regular succession of small
bubbles, the following experiments can be at once conducted:

(1) Substitute for the fresh water some which has been boiled a few
minutes before, and then allowed to completely cool: by the boiling,
all the carbonic acid has been expelled. If the plant is immersed in
this water and exposed to the sun's rays, no bubbles will be evolved;
there is no carbonic acid within reach of the plant