48 PISTILS AND STAMENS 
pistil of a Ben Davis Apple blossom may be pollinated: (1) with 
pollen from the same flower; (2) with pollen from another flower 
in the same cluster; (3) with pollen from a flower on another 
branch; (4) with pollen from another Ben Davis tree located in 
the same or a neighboring orchard; or (5) with pollen from a 
Jonathan or some other different variety. In case of fruit trees 
horticulturists sometimes consider the pistil of a blossom self- 
pollinated if the pollen comes from the same flower, from another 
flower on the same tree, or from another tree of the same kind, 
and consider the pistil cross-pollinated only when the pollen 
comes from another variety of fruit tree. Corn breeders speak 
of self-, close-, and cross-pollination. Pollination resulting from 
the pollen falling from the tassel to the silks of the same plant is 
called self-pollination. Pollination in which the pollen from one 
plant falls on the silks of another plant is called close-pollination 
if both of these plants came from kernels taken from the same 
ear, but cross-pollination if these plants came from kernels taken 
from different ears. In case of cross-pollination, the plants may 
be of the same variety or of different varieties. 
The Amount of Pollen Required for Good Pollination. — One 
pollen grain is required to fertilize each ovule, and, therefore, a 
pistil with many ovules requires many pollen grains for good 
pollination. In Corn, Wheat, and Oats where there is only one 
ovule, one good pollen grain on the stigma is sufficient, although a 
large number is usually present. Due to the great waste of pol- 
len during transportation, much more is produced than is really 
needed. A medium-sized plant of Indian Corn produces about 
50,000,000 pollen grains or about 7000 for each silk. Many of 
these never reach a silk, and of the many that do all, except the 
one that reaches the ovule first with its tube, accomplish nothing. 
On the stigma of the Red Clover, although each pistil has only 
two ovules, there are often as many as 25 pollen grains, 23 of 
which are wasted. 
On the other hand, in flowers where the ovaries contain numer- 
ous ovules, as in Tomatoes and Melons, it often happens that 
not enough pollen reaches the stigma to effect fertilization in all 
the ovules. In the Tomato, for example, an ovary may contain 
as many as 200 ovules, in some of which fertilization may not 
occur because of insufficient pollination. Evenin Beans, Apples, 
and Pears, where the ovules are not numerous, one often finds in 
