Hayes and Garber - Cucurbit Breeding

18 BREEDING CROP PLANTS
pair being obtained from the male parent and the other from the
female parent. At the formation of the sexual cells, or at reduction
division, one member of each pair of chromosomes passes to
each daughter cell thus reducing the chromosome number to half
that in the body cells. Following
an equating division whereby each chromosome is
this reduction division there is
qualitatively
FIG. 4. Anther and pollen of the lily.
A, Mature anther, showing the four locules, or chambers, containing pollen grains: the
anther opens lengthwise on both sides along the lines of cells shown at z; B, stages in the
formation of pollen grains in a group of four (tetrad) within the pollen mother cell; C,
mature pollen grain with early stages in the development of the male gametophyte; tube
t,
nucleus; g, generative nucleus. (After Bergen and Davis.)
equally divided. This results in the formation of the male or
female sexual cells or gametes as they are called (see Fig. 3).
The male sexual cells are produced in the anthers and are
carried in the pollen grains. A mature pollen grain contains two
nuclei, a tube nucleus and a generative nucleus (see Fig. 4).
After the pollen grain falls on the pistil the tube cell