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-polKnation 

 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 foi* 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 fertiHzation may not 

 occur because of insufficient pollination. Even in Beans, Apples, 

 and Pears, where the ovules are not numerous, one often finds in 



