ping
quality, properly to pass through vinous fermentation, or even to make
a good unfermented grape-juice. In the uneven topography of this
continent, it is not possible to state the range in latitude in which
grapes can be cultivated to advantage, for latitude is often set aside
by altitude. Thus, isothermal lines, or lines of equal temperature,
are much curved in America and do not at all coincide with the
parallels of latitude.

Other factors, of course, than length of season enter into the
ripening of grapes. The daily range in temperature, not always
dependent on latitude, affects ripening. Cool nights may offset warm
days and delay ripening. Certainly rains, fogs and humid air delay
maturity. The bottom heat of loose, warm, dry gravelly or stony soils
hastens maturity. Sunshine secured by a sunny aspect or shelter
hastens maturity.

_The seasonal sum of heat._

Successful cultivation of the grape depends on a sufficient amount of
heat during the summer season. The theory is that buds of the grape
commence to start when the mean daily temperature reaches a certain
height, and that the sum of the mean daily temperature must reach a
certain amount before grapes ripen. Manifestly, this sum must vary
much with different varieties, low for the earliest sorts, high for
the latest. There have been many observations as to the temperatures
at which buds of the grape start growth, so that it is now known that
the temperature varies in accordance with locality and degree of
maturity. Roughly speaking, grape buds start at temperatures from 50 deg.
to 60 deg. F. The seasonal sum of heat for ripening is probably 1600 to
2400 units. A variety ought not to be planted, therefore, in a region
in which the average seasonal sum of heat is not sufficiently high.
The seasonal sum of heat can be determined for a locality from data
published by the United States Weather Bureau; and by comparing with
the sum of heat units in localities where a variety is known to
thrive, the grape-grower can determine whether there is sufficient
heat for any particular variety.

The grape seldom suffers from hot weather in a grape region. The fruit
is sometimes scalded in the full blaze of a hot sun, but the ample
foliage of the vine usually furnishes protection against a burning
sun. At maturing time, the heat of an unclouded sun, if the air
circulates freely, insures a finely finished product. Deep planting
helps to offset the harmful influences o