DEVELOPMENT OF PLANTS 



197 



gamete is found in a similar branch which becomes rather egg- 

 shaped and at maturity opens at the beaked end (Fig. 114, B). 

 A single-celled female gametangium is called an o5gonium and 

 the female gamete is frequently referred to as the oosphere or 

 egg. The male gametes are discharged a few minutes after the 

 oogonium opens, when they swarm about the open end of the 

 female gametangium and readily enter it. As soon as fusion has 

 been effected the gametospore becomes invested with a thick wall 

 and in this condition can endure a limited drought. In germi- 

 nating it develops directly into a' new plant. This feature of the 



Fig. 115. Growth and asexual reproduction of Oedogonium: A, young 

 plant showing basal cell modified as a hold-fast. B, two cells of a filament, 

 in one of which a zoospore is forming and the other cell has opened, per- 

 mitting the escape of the zoospore shown at C. D, zoospore at rest. It 

 becomes attached to an object at its colorless, ciliated end. E, later stage 

 in the germination of the zoospore. — ^After ^^'est. 



life history of Vaucheria, therefore, appears as of a more primitive 

 nature than in the case of Ulothrix. In the following studies you 

 will repeatedly notice variations of this nature. In the develop- 

 ment of plants advances are often confined to one or another 

 feature of their organism which may become highly developed 

 and specialized; at the same time one or more features may be 

 retained that have been subject to little or no variation and 

 which, therefore, remain in a primitive state. 



71. Other Members of the Green Algae. — There are several 



