THE FUNGI 227 



The germination of the oospore takes place after a long 

 interval, and only when it is brought into contact with 

 water. The process shows very remarkable variations, 

 both among different species and among individuals of 

 the same species, comparable to the variations in the 

 behaviour of the asexual sporangium described above. 

 In some cases the outer thick layers of the oospore 

 membrane are burst, and the contents, surrounded by a 

 delicate cell-wall, grow out into a hypha, thus starting a 

 new mycelium directly. In other cases the process 

 begins in the same way, but the hypha at once forms a 

 sporangium, into which the whole contents pass, dividing 

 up into a number of zoospores (see Fig. 93, C). In a 

 third mode of germination, the formation of the hypha 

 is suppressed, and the zoospores are produced in the 

 interior of the oospore itself. The zoospores swim about 

 like those formed on the vegetative plant, and on coming 

 to rest reproduce the ordinary form of the Fungus. 



These are differences to which considerable systematic 

 importance would be attached in other groups of plants ; 

 here the different modes of germination are not even 

 constant for the species, but appear to depend on the 

 nutrition, direct germination taking place when food is 

 abundant, while under less favourable conditions zoo- 

 spores are formed at once, thus allowing additional 

 chances of a suitable habitat being reached. We may 

 say, then, that in a Fungus such as Pythium, the ex- 

 ternal circumstances determine whether anything like an 

 alternation of generations takes place or not. 



Pythium and its allies stand nearer to the Algae than 

 any other Fungi ; in fact they were once themselves placed 

 in the former class, and it is evidently with non-cellular 

 Algae of the type of Vaucheria that they have the closest. 



