without pollen
from another flower.
_Sterile_: Said of a flower without or with abortive pistils.
_Perfect_: Said of a flower having both stamens and pistils.
_Imperfect_: Said of a flower wanting either stamens or pistils.
_Peduncle_: The stalk of a flower-cluster.
_Pedicel_: The stalk of each particular flower.

The time of bloom is an easy mark of distinction between several
species of grapes and helps to distinguish varieties in a species as
well. Most species of grapes bear fertile flowers on one vine and
sterile flowers on another and are, therefore, polygamous-dioecious.
Sterile vines bear male flowers with abortive pistils so that, while
they never produce fruits themselves, they usually assist in
fertilizing others. Fertile flowers are capable of ripening fruits
without cross-pollination. Vines with female flowers only are seldom
found. In most species of the grape, plants with sterile flowers and
those with complete flowers are found mixed in the wild state, but
usually only the fertile plants have been selected for cultivation.
Plants raised from seeds of any of the species, however, furnish many
sterile vines.

[Illustration: FIG. 53. The grape flower. I. Opening bud showing the
way in which the cap becomes loosened at the base. II. Diagrammatic
illustration of grape stamens.]

The degree of fertility of blossoms is also a fine mark of distinction
in species and varieties of the grape. Fertile vines are of two kinds
in most species. The flowers on one kind are perfect hermaphrodites,
while in the other kind the stamens are smaller and shorter than the
pistil and eventually bent down and curved under. The two kinds of
stamens are shown in Figs. 53 and 54. These may be called imperfect
hermaphrodites since they are seldom as fruitful as the perfect
hermaphrodites unless fertilized from another plant. Examined with a
microscope, it is found that self-sterile plants usually bear abortive
pollen and that the percentage of abortive pollen grains varies
greatly in different varieties. The upright or depressed stamen does
not always indicate the condition of the pollen, since there are many
instances in which upright stamens bear impotent pollen and
occasionally the depressed stamens bear perfect pollen.

[Illustration: FIG. 54. Grape flowers. _Left_, upright stamens of
Delaware; _right_, depressed stamens of Brighton.]

_The leaf._

_Blade_: The expanded portion of