to the grape-grower,
the blooming period being so late that grapes are seldom caught by
frost, until the discovery was made that many varieties of grapes are
unable to fertilize themselves, and that failure of crops of these
varieties was often due to the self-sterility of the variety. Until
this discovery, the uncertainty attending the setting of the grape in
these varieties was one of the discouragements of grape-growing.
Following investigations of the self-sterility of the tree-fruits, an
investigation of the grape showed that the vines of this fruit are
often self-sterile. This knowledge has in some degree modified the
planting of all home collections and has more or less affected the
plantings of commercial sorts.

Varieties of American grapes show most remarkable differences in the
degree of self-fertility. Many sorts fruit perfectly without
cross-pollination. Others set no fruit whatsoever if cross-pollination
is not provided for. Most varieties, however, are found in groups
between the two extremes, neither self-fertile nor self-sterile.
Figure 51 shows staminate and perfect clusters on one vine. Some
varieties show no variation in the degree of self-sterility or
self-fertility; others behave differently in regard to these
characters under different environment. Now and then the widest
variations are to be found in a variety in respect to self-fertility.

[Illustration: FIG. 51. Staminate and perfect clusters on one vine;
_right_, staminate; _left_, perfect.]

Following the lead of Beach at the New York Agricultural Experiment
Station, several workers have made careful studies of the
self-fertility of the grape, and now the cultivated varieties of
native grapes are divided into four groups in accordance with the
degree of self-fertility. Class I includes self-fertile varieties
having perfect or nearly perfect clusters; Class II includes
self-fertile varieties having clusters loose but marketable; Class III
includes varieties which are so imperfectly self-fertile that the
clusters are generally too loose to be marketable; Class IV includes
self-sterile varieties. The following is a list of commonly cultivated
grapes classified according to the divisions just given:

CLASSIFICATION OF GRAPES ACCORDING TO SELF-FERTILITY

CLASS I. Clusters perfect or varying from perfect to somewhat loose.

Berckmans
Bertha
Cottage
Croton
Delaware
Diana
Etta
Janesville
Lady Washing