New-York tribune., 1873-03-15

noss 10 the stems and elasticity and tenacty .o a..
leaves. When grape vines, for example, which ~
growing in a sandy SOIL have access 10 potash -
abundance, the leaves will appear az tonog -
leather and no mildew rust will ever aaec, ,l1
foliage nor injuTe the fruit.
RIsIERs RESEARCHES on EVAPORATION ypo,.
PiANTs.--The following propositions are presented
by Mr. T.. Risler as the results of his researches On
the evaporation from plants: Evaporation from.
plants is not lessened when the surrounding Al, {,
saturated with aqueous yapor. Absorption Of u,e
vapor in the air by leaves has never been Oh
served Plants in general eyaporate but very little
during the night time. All plants evapoFate more in
the sun than in the shade. With luzene the qnar
tty eyap0rated in the sun is four times AZ great a.
in the shade, even when the difference in .snnsr,
ture ia not very considerable Thus, the direct in
luence of light, independent Of its heat il demon
strated The yellow rays OF the spectrum are mo-.
active. With Indian corn the difference 0f evapor,
ton in sun aud shade is still larger than with uzene
while some plants are much less influenced the Wil.
low for instance shows very little difference Tbi.
is, in Mr.. Rsler's opinion, one Of the reasons why
some plants thrive better in shade than Others Hu
midity or moisture of the air exeTts appreciabe
influence upon evaporation, although il was asceF-
tanned that evaporation increased with tho approach
of storm, even when heat and light had not in.
creased The moisture Of the soil is Of the
greatest importance. After rain, or water
ing the evaporation increases; with continued
dryness the plants wilt, but frequently recover with
the disappearance of the sun, when the absorption
of water by the roots becomes greater than the
evaporation by the leaves. When a large volume q
soil is accessible to the plants the supply Of moisture
is larger and more regular. Hence these practical
conclusions: crop requires the more water the
more densely it is planted. When older aud more
vigorous plants stand in the same soil with young
and less developed ones, the former will take up
more water than the latter, and these will suffer II
the moisture does not suffice for both. Also with
the water the stronger plants take more Of the
nourshment in solution; hence the injurious infg-
ence Of trees and weeds upon young plantations
The water taken from that portion of the ground
with which the roots are in immediate contact is
placed by the surrounding soil so as to establish an
equilibrium of moisture in accordance with the laws
of diffusion soil will suffer less from dryness tue
better it is manured. With an equal surface, the
evaporation from the young leaves is less than from
those that are fully developed. Mr. Rlser, from hs
careful experiments and observations, has also de-
duced the absolute amount of evaporation for sew
eral important crops and ascertaned that, IN many
cases. the quantity Of water eyaporated Is much
greater than that obtained from rain during tie
growing season, the plants drawing their supply
from the moisture previously accumulated in the
soil Hence the value of deep culture, which ex-
tends the area accessible to the roots. Forests eya
crate much less water than cultivated land: they
consume in fact not one-haf of the fallen rain and
thus serve as source of supply for the adjoining re-
gions Their ramifed roots prevent a too rapid rush
of the water, and the washing Of the surface SOIL
&c: but Mr. Riser maintains that it is by no means
proved that woods actually increase the rainfall by
contributing in any way to the condensation Oh
atmospleric humidity.