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 CHAPTER XIX

THE FLOWER—FERTILIZATION AND POLLINATION

Fertilization.—Seeds result from the union of two elements or parts. One of these elements is a cell-nucleus of the pollen-grain. The other element is the cell-nucleus of an egg-cell, borne in the ovary. The pollen-grain falls on the stigma (Fig. 193). It absorbs the juices exuded by the stigma, and grows by sending out a tube (Fig. 194). This tube grows downward through the style, absorbing food as it goes, and finally reaches the egg-cell in the interior of an ovule in the ovary (Fig. 195), and fertilization, or union of a nucleus of the pollen and the nucleus of the egg-cell in the ovule, takes place. The ovule and embryo within then develops into a seed. The growth of the pollen-tube is often spoken of as germination of the pollen, but it is not germination in the sense in which the word is used when speaking of seeds.

—B, escaping from anther; A, pollen germinating on a stigma. Enlarged.

Better seeds—that is, those that produce stronger and more fruitful plants—often result when the pollen comes from another flower. Fertilization effected between different flowers is cross-fertilization; that resulting from the