196 SEXUAL REPRODUCTION OF VAUCHERIA 



injury to the filaments. Asexual reproduction is effected by very 

 large zoospores which are developed in the enlarged extremities of 

 the filaments (Fig. ii^, B). These tips are cut off by a transverse 

 wall and a single zoospore escapes through an opening in the 

 tip of the sporangium thus formed. The entire surface of the 

 zoospore is clothed with cilia arranged in pairs, each pair being 

 associated with a nucleus so that the zoospore resembles the 

 motile colonies previously noted (Fig. 113, C). After a very 

 short motile period, the zoospore comes to rest and grows into 

 the characteristic tubular plant (Fig. 113, D). When the plants 

 are exposed to too dry conditions, the tips of the filaments often 



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, permitting the 

 escape of the male gametes and the fertilization of female gamete. C, gam- 

 etospore detached from the filament. 



enlarge and finally become detached as motionless spores that 

 germinate when conditions are again favorable. 



The male and female gametes are produced in gametangia that 

 are formed from short branches. The males are developed in 

 large numbers in curved branches that become cut off from the 

 filament by a cross wall (Fig. 114, A) and the gametes finally 

 escape through an opening that forms at the apex of the branch. 

 A gametangium that produces clearly differentiated male gametes 

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

 frequently called antherozoids or sperms. A single female 



