116 MONOCOTYLEDENOUS ANG10SPERMS 



tained within the embryo sac. Three of these cells pass to 

 the end of the embryo sac nearest the micropyle. The two 

 outer cells are the synergids. They help to nourish the 

 pollen tube and direct it toward the inner or egg cell. Two 

 cells pass to the center of the embryo sac and fuse to form 

 the endosperm nucleus. The three remaining cells pass to 

 the opposite end of the embryo sac and are called the anti- 

 podal cells. 



The embryo sac with the seven cells described above is 

 the female gametophyte. In all the monocotyledons and the 

 dicotyledons, the next higher group, no archegonia are 

 found. 



Structure of the Stamen. Each stamen consists of & filament 

 or stem, and an anther. The anther consists of two double 

 pollen sacs separated by a continuation of the filament. The 

 pollen sacs contain the spore mother cells each of which divides 

 to form four pollen grains. 



Structure of the Pollen Grains. Each pollen grain consists 

 of an outer wall or exine, which is reticulate or netlike in 

 structure, and a thin inner wall or inline which surrounds 

 the protoplasm and nucleus. 



Pollination. Bees and other insects visit the flowers to 

 secure the nectar or sugary solution secreted by the nectar 

 glands. While the insect is securing the nectar, it moves 

 the stamens and pollen is dusted on its body. The stigma 

 of another flower, which the insects afterwards visits, rubs 

 against its body and receives some of the pollen grains. In 

 this way cross-pollination is effected. 



Development of the Male Gametophyte. The pollen grain 

 divides to form the male gametophyte which consists of a 

 tube cell and an antheridial ceil. The tube cell develops the 

 pollen tube which breaks through the exine and grows down 

 through the tissues of the style and nucellus to the embryo 



