Vermont phÅ“nix. [volume] (Brattleboro, Vt.) 1834-1955, 1885-07-17
Hpaw and Frost,

Every farmer knows that dew is present be.
fore the sun rises during certain seasons even
in the dryest of periods, and tho fact that
frost is but frozen dew is also familiar TO all
For valuable information in regard to the for.
nation of dew and its relation to plants we
are indebted TO Professor Puryear, of Virgin
ia, from whose article in the American Far
mer the following is condensed 1t is obvious
that during the first days and weeks of plant
life dow is most needed because at that time
the rootlets must get their supply of moisture
from near the surface, which is liable to be-
come dry. Nature, however, provides for
this Objects to have dew deposited upon
them must become sufficiently chilled at night,
by the radiation of heat, to condense the
aqueous vapor of the atmosphere. All objects
must be reduced in temperature TO the dew
point. This is much more easily accomplish
ed in May than in August, for two reasons.
In May the sun is not so hot, nor docs it
shine so long, as in August, nor is the tenn
peTature of the atmosphere and of the earth's
surface as elevated in the day during May as
in August To got dew objects have to sink
at night to the dew point to n much lower
temperature in May than in August, for in
the latter month they must sink from 80 or
9Oo, and during the former from GO to 707, TO
get to the dew point In order, therefore, to
get copious deposit of dew, plants have less
work to do in spring or fall than in summer,
and they have more time to do it in, and
hence the abundant deposit in the spring and
fall and the scant supply in midsummer.
Devils less needed in summer than in spring
or fall, for the reason that as the season adj.
vances the roots are striking down deeper
and deeper every day. Rain may not fall for
sveeks yet the roots are getting moisture from
below all the while, but when plants have just
completed termination, and when their roots
are near the surface, drought of few days
would be fatal but for the nightly deposits of
dew. The benefits derived from the heavy
dews in the early fall are reaped by the young
plants of wheat, rye, turnips and the grasses.
) 10 get copious deposits of dew the plants
must be chilled but If chilled too much the
dew il frozen into frost and vegetable vitality
destroyed To secure a benefit danger ia
incurred but in the very process of securing
the benefit the danger is weakened VapOr
is water with certain amount of heat in ii
heat in the latent state. When we con-
d6nse this vapor the heat, before latent, il
evolved or given out. When aqueous vapor
IL in the process of condemnation into dew all
its latent heat (the heat that made it vapor)
Is evolved on the surface whore the conden-
Ratlon takes place. Consider a fine tobacco
field, its broad leaves ripening in the mild
September The leaves lose heat rapidly by
radiation, they become chilled, and the aqne-
GUS vapor is condensed into dew, but in such
act its latent heat il evolved and warns up
the leaves, thereby lessening the liability of
injury from frost The atmosphere immedi.
ately brooding over the leaves is sensibly
warmer than the atmosphere elsewhere. II
the same amount of water be sprinkled at
nightfall the cold may be sufficient to freeze
it, but not sufficient il this water has been
condensed from vapOr, for the process of
condemnation throws out, in sensible form,
the latent heat of the vapor.
The process of aqueous condemnation, or
dew formation, pOstpOnes the appearance of
frost. Plants must become chilled TO form
dew, but in such condemnation heat is thrown
out to prevent frost This battle goes on for
weeks, until at last the increasing length and
GOODNESS of the nights get the advantage, for
then the cold becomes too great to be counter
balanced by the heat evolved from aqueOus
condemnation the dew freezes as it falls, and
the plant il killed. The effects of moisture
through the agency of rains and dews is not
always the same. In the case of tobacco lit
tie rain and copious dews in the early fall
make tobacco leaves thick, heavy and oily,
and its quality is improved by comparatively
dry weather and heavy dews. Dews, then,
to some extent, furnish TO all plants in the
earliest stage of their growth, small but fire.
qnent supplies of moisture, and enables some
Of them, such az tobacco, to attain, while APP
preaching maturity, their highest perfection.