THE SPERMATOPHYTES 461 
pollen chamber and micropyle. Two to six archegonia are 
developed from the prothallial tissue just beneath the archegonial 
chamber. Each archegonium consists of two neck cells protruded 
into the archegonial chamber and a large ovum embedded in 
the prothallus. The contents of. the mature embryo sac, therefore, 
represents the female gametophyte. 
FERTILIZATION.—It will be recalled that at the time pollina- 
tion was effected, the male gametophyte’ had assumed the char- 
Pollen Chamber _Integument Nucellus. - 
Zz ee Integument { 
Microgametophyte Macrogametophyte ; 
Fic. 348.—Zamia. Stages in the development of a megasporangium and a 
macrogametophyte (megagametophyte). A, at the time when the macrospores 
(megaspores) are formed. B, after the germination of one macrospore to form a 
macrogametophyte. C, at the time of gametic union. (From ‘A Textbook of Gen- 
eral Botany” by Smith, Overton et al., the Macmillan Co., Publishers.) 
acter of a pollen tube (see Fig. 348) containing a prothallial 
cell, stalk cell, and two antherozoids which lay in the pollen 
chamber. Several of these are usually present. Now, when the 
eggs are mature, the tube grows through the nucellus to the arche- 
gonial chamber and the end of the tube bursts. The antherozoids 
of the several tubes move about in the fluid of the chamber and 
some of these pass through the necks of the archegonia, one 
uniting with each egg. The sperm nucleus then unites with the 
egg nucleus forming a zygote. 
SEED DEVELOPMENT.—The zygote, through repeated division, 
forms a young sporophyte or embryo Kamia in the upper end of the 
female gametophyte (prothallus) of the ovule. This, by the 
elongation of several cells, becomes differentiated into a slender 
1 Microgametophyte is another name for male gametophyte, and macrogametophyte 
a synonym for female gametophyte. : 
