176 



SEXUAL REPRODUCTION 



A gametangium that produces clearly differentiated male gametes 

 is called an antheridium (pin. antheridia) and the gametes are 

 frequently called antherozoids or sperms. A single female 

 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 oogonium 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 

 life history of Vauchcria is therefore of a more primitive nature 

 than in the case of Ulothrix. In the following studies vou will 



Fig. 114. Sexual reproduction of Vaucheria: A, portion of a filament 

 that has formed two branches which have grown into a male, an, and 

 female, og, gametangia. B, later stage, the gametangia have opened, per- 

 mitting the escape of the male gametes and the fertilization of female 

 gamete. C, gametospore detached from the filament. 



repeatedly notice variations of this nature. In the development 

 of plants advances are often confined to one or another feature 

 of their organism which may become highly developed and spe- 

 cialized; at the same time one or more features may be retained 

 that have been subject to little or no variation and which, there- 

 fore, remain in a primitive state. 



