Vaucheriacece 113 



this part which breaks up into the antherozoids (or spermatozoids). 

 The latter are extremely minute, each one consisting of a small 

 amount of protoplasm surrounding a nucleus and possessing two 

 cilia. The cilia are attached far apart and point in opposite 

 directions. (Fig. 43 A, an.) The antherozoids swarm for a short 

 time within the antheridium, which soon opens at the apex and 

 sets them free. A certain amount of unused protoplasm is 

 expelled with the antherozoids and another portion is left behind 

 in the antheridium. 



The antherozoids swarm near the opening of any oogonium 

 they may happen to reach and frequently several of them enter 

 the oogonium. One of them fuses with the oosphere at the region 

 of the receptive spot and its nucleus travels through the protoplasm 

 of the oosphere until it reaches the single nucleus of the latter. 

 The male and female nuclei then unite and fertilization is effected. 



The fertilized ovum or oospore now invests itself with a cell- 

 wall of considerable thickness and undergoes a prolonged rest. 

 The oospores can withstand a certain amount of desiccation, and on 

 germination they give origin to a new plant without any alternation 

 of generations. 



Genus Vaucheria DC., 1803. This is a widely distributed 

 genus of Alg?e the filaments of which are interwoven to form 

 compact, mat-like masses, either on damp earth, or in fresh or salt 

 water. They most commonly occur in situations where they are 

 subject to the splashing or trickling of water, although some 

 habitually occur on damp ground or are entirely submerged. They 

 are most abundant in the earlier months of the year. The filaments 

 are coarse and thick, consisting of large ccenocytes, which some- 

 times reach 30 cms. in length, a.nd their numerous chloroplasts 

 give them a dark green colour. They are very sparsely branched, 

 and some species rarely exhibit any branching except in connection 

 with the formation of the sexual organs. Dioecious species of the 

 genus exist, but in most others the antheridia and oogonia are 

 developed in close approximation on the same filament. The 

 filaments are sometimes subject to the attacks of the Rotifer 

 Notommata Wemeckii, which produces irregular gall-like swellings. 



V. sessilis (Vauch.) DC. is perhaps the commonest species of the genus, 

 being widely distributed in damp and wet situations in the neighbourhood of 

 streams, cataracts and boggy springs ; thickness of filaments 65 80 p (tigs. 42 

 C and E ; 43 A and B). V. geminata (Vauch.) DC. also occurs in similar 



w. A. 8 



