STEUCTUKE AND WORK OF PLANTS 



21 



stamens, easily recognized Ijy their slender stalks and the en- 

 larged tips which are known as the anthers. Within the anther 

 is the pollen or pollen grains. At the tip of the flower, within 

 the group of stamens, is the pis- 

 til, consisting of one or more 

 units or carpels. Often the tip of 

 the pistil is expanded, and some- 

 times divided into two or more 

 short branches, this portion being 

 called the stigma; the elongated 

 part of the pistil is the style, and 

 the swollen base is the ovary, 

 so called because it contains the 

 ovule or ovules. The ovules are 

 the developing seeds. 



22. Flowers and seeds: seed 

 formation. The ovules begin their 

 development withui the ovary, 

 but cannot alone form mature 

 seeds which will grow into new 

 plants. Some of the pollen from 

 the anther of the same or an- 

 other flower falls upon the stigma 

 (Figs. 13, 14, and 15). From one 

 or more of these pollen grains 

 there grows down through the 

 style into the ovule an extremely 

 small tube. Inside this tube are 

 carried some of the cellular con- 

 tents of the pollen grain, which 

 meantime have divided into three 

 cells. One of these cells thus 

 carried into the ovule by the pollen tube unites with a special 

 egg cell that is formed withm the ovule (Fig. 14). The cell 

 that is made by the union of the one from the ovule and the 

 one from the pollen tube grows into the new plant within 



Fig. 14. A diagram of a pistil 

 (carpel) 



Within the cavity of the ovary is an 

 ovule (n), and within the ovule is 

 an embryo sac. At the free end of 

 the ovule is the micropyle (m). In 

 the end of the embryo sac near the 

 micropyle is the egg (egg) with two 

 other nuclei lying close to it ; in the 

 center of the sac is the endosperm 

 nucleus (en) \ and at the other end 

 are the antipodal nuclei (a) . Pollen 

 grains (p) are on the stigma, and 

 from one is shown a pollen tube 

 which has grown down to the egg 



