Hayes and Garber - Cucurbit Breeding

PLANT GENETICS 19
elongates, forming a pollen tube which passes down the style.
This tube grows through the tissue of the pistil and reaches the
embryo sac. The generative nucleus passes into the pollen tube
and divides, forming two nuclei which are the male gametes.
The pollen tube grows through the tissues of the pistil until it
reaches the embryo sac, and the tip of the tube breaks after it
penetrates the wall of the embryo
life
sac. In fertilization one of
FIG. 5. Longitudinal section of the lower portion of the embryo sac of
maize at the time of fertilization; pn, polar nuclei fusing; sn, sperm nucleus
fusing with a polar nucleus, pn', e, egg; sn, sperm nucleus in the egg; pt, pollen
tube; syn, synergid; v, vacuole. (After Miller.)
these gametes of the pollen tube unites with the egg cell to form
the embryo of the seed and the other unites with two polar nuclei
to form the endosperm (see Fig. 5).
If we represent the chromosome number of each body cell by
2x, each gamete would be represented by x, the embryo formed
by the union of the generative cell with the egg cell would be
2x and the endosperm tissue 3z.