Perrysburg journal. (Perrysburg, Wood Co., O. [Ohio]) 186?-1965, 1874-03-06
Influence of the Winds on Vegetation.

A WRITER in the American Exchange
and Repieto has recently called attention
to the extent to which vegetation is de-
pendent for its. life and growth on the
winds, by which alone vapor and rain are
conveyed from the place of formation and
distributed over the earth. While animal
life is able, by its powers of locomotion,
to seek the necessary moisture, the vege-
table world, were it not for the air cur
rents, would perish from the earth. This
destruction would obviously be very rapid
as the quantity of the solid matter in a
plant is small compared to that of the wa
ter And therefore the moisture of the
soil is more necessary to vegetable growth
than are the mineral constituents; and the
water not only provides the means OF
growth of the plant, but also accelerates
the decay by which the solid constituents
are returned to the earth, to rise anew in
the plant life of another generation.
For the evaporation by which water is
raised into vapors, for the subsequent dis
tribution of that vapor and for its con-
densation in the falling rain Nature has
provided the ceaseless, omnipresent aerial
currents. The magnitude of this process
of exhaustion and restitution may be esti-
mated from the fact that the total daily
discharge of all the rivers in the world in
to II the oceans is but the quantity of rain
which has fallen in single day. The suns
heat falling on water surface converts a
part of it into vapor, which rises into
and is diffused through the atmosphere
in obedience to the laws that govern the
mingling of gases. Within certain limit
this vapor remains invisible, and cannot
be distinguished from the main bulk of
the air. At every temperature the air is
capable of holding in an invisible condi-
tion a definite quantity of vapor. The
warmer the air, the more it can hold. But
for every temperature there is a point
beyond which it is impossible for more
vapor to pass it. This point is called the
point of saturation, or the dew point.
When the air has reached its dew point,
and its temperature is increased, no Wis
ible effect is produced-its capacity for
moisture is simply increased; but if its
temperature be lowered, then it is no
longer capable of holding all its moisture
and the surplus becomes visible in some
form or other of precipitation, namely, as
fog, cloud, dew, rain, hail, or snow. In
order to account, then, for any precipita-
ton of moisture, it is necessary first that
a sufficient quantity of vapor pass into
the air to bring it to its dew point, and
then that the temperature be lowered.
The quantity of moisture thus precipi.
tated will clearly depend upon two cir
cumstances, namely, the temperature of
the air when the dew point is reached,
and the temperature to which it was sub
sequently lowered. The higher the one
and the lower the other, the greater will
be the precipitation.
The means by which the lowering of
the temperature can be accomplished are
varied. A warm, vapor-laden air may
blow into cold region, and thus have
its temperature lowered sufficiently be-
low the dew point to give considerable
rainfall. A cold wind may mingle with a
warm one, and thus produce a moderate
shower; or powerful ascending currents
may carry the moisture of the lower strata
into the upper regions Of the atmosphere,
where the temperature is very low.
The deposition of the moisture of the
air is, then, in all the cases we have con-
sidered, referable TO atmospheric motion;
for upon it will depend the presence or
the absence of moisture in any region,
and consequently the presence or absence
of vegetable life. The ocean of aqueous
vapor partakes perfectly of the move
ments of the atmosphere. 1t in fact de-
rives its movements mainly from those of
its bulkier neighbor. 1t is to the motion
of the winds, then, that we must look for
the explanation of the peculiarities that
attend the distribution of moisture.-Sci-
entifc American.