110 A TEXT-BOOK OF BOTANY 



formed a single large gamete, which remains in the cell that 

 produces it. This large gamete, which remains passive, is 

 the female gamete or egg, and the globular cell that produces 

 it is the oogonium (egg-case). In the figure (Fig. 99, A 

 and B) these large eggs are seen packed with roundish 

 masses of reserve food. 



Other cells, either in the same filament or in some other 

 filament, differ from the ordinary cells in being much 

 shorter (Fig. 99, A, b, and B, a). In each of them one or 

 two gametes are formed and are set free, swimming about 

 like small swimming spores (Fig. 99, B, b). These active 

 gametes are the male gametes or sperms, and the short cell 

 that produces them is the antheridium. 



The sperms swim actively about in the vicinity of an 

 oogonium, and sooner or later one enters through an open- 

 ing in the oogonium wall and fuses with the egg (Fig. 99, 

 B, c). As a result of this act of fertilization an oospore 

 is formed that soon organizes a firm wall about itself (Fig. 

 99, A, c). This firm wall indicates that the oospore is not 

 to germinate immediately, but is to be protected through an 

 unfavorable season, such as failure of food supply, cold, 

 or drought. 



It is evident, therefore, that although both the swimming 

 spores and the oospores are able to produce new plants, the 

 former germinate immediately and enable the plant to 

 spread during the growing season, while the latter last 

 through the winter when the parent plants have perished, 

 and form new plants in the new growing season. 



The most important fact illustrated by (Edogonium is 

 that the gametes are not alike, as in Ulothrix and Clad- 

 ophora, but have become very unlike. One of them (the 

 egg) is relatively large and passive; the other (the sperm) 

 is relatively small and active. In this case, therefore, the 

 two sexes are apparent, and we recognize male and female 

 gametes. 



