f warm climates.

_Humidity of summer weather._

The grape is very sensitive to moisture conditions, and grows best in
regions where the summer rainfall is comparatively light. A damp and
cloudy summer brings disaster to the vineyard in several ways; as
small growth of vine, small set of fruit, a crop of poor quality, and
the development of the several fungous diseases. Although the grape
stands drought, a superfluity of moisture in the soil may do little
harm, as is shown in irrigated vineyards, but a humid air is fatal to
success especially if the air is both warm and wet. Moist weather
during the time of maturity is particularly disastrous to the grape,
as are frequent fogs. Cold wet weather in blooming time is the
grape-grower's vernal bane, since it most effectually prevents the
setting of fruit. It may be laid down as a rule that the grape lives
by sunlight, warmth and air--it often thrives on the desert's edge.
These considerations make it manifest that the monthly and seasonal
means of precipitation must be considered in selecting a locality to
grow grapes.

_Spring and autumn frosts._

The average date at which the last killing frost occurs in the spring
often determines the limit in latitude at which the grape can be
grown. Even in the most favored grape region of the continent, killing
frosts occasionally destroy the grape crop, and there are few seasons
in which frost does not take some toll. Thus on May 7, 1916, frost all
but ruined the crop of wine- and table-grapes in the great grape
region of northern California where frosts are seldom expected in May.
Little or nothing can be done to protect grapes from frost. Windbreaks
as often favor the frost as the vine, and smudging or heating the
vineyards is too expensive to be practical. In growing grapes,
therefore, the commonly recognized precaution of selecting a site
near water, on slopes or in a warm thermal belt must be exercised.

The limits of grape culture are also determined by early autumn
frosts. The grape stands two or three degrees of frost, but anything
lower usually destroys the crop. Here, again, the only precaution is
to take pains in selecting the site.

_The use of weather data and dates of life events of the grape._

These considerations of length of season, humidity and spring and fall
frosts make it plain that the grape-grower must synchronize these
phases of climate with the life events of the grape. In particular, he
must study