THE FUNGI 221 



2. KEPRODUCTION 

 a. Asexual 



The hyphse which are to produce the asexual organs 

 of reproduction grow out from the host into the open 

 air. They there form a number of spherical sporangia 

 which are terminal, being seated on the ends of short 

 branches or of the main hyphoe (see Fig. 93, A). The 

 sporangia are beaked at the apex, and, when ripe, the 

 entire protoplasm passes out into the beak, which swells 

 up into a bladder-like sac (see Fig. 93, B). The whole 

 process can only go on when there is water enough 

 to immerse the sporangia. The contents of the sac 

 now divide up into a number of membraneless cells 

 which become zoospores, each bearing two cilia. The 

 zoospores escape and swim away through the water. 

 After some time they come to rest and germinate, 

 producing a hypha, which finds its way into a fresh 

 seedling as soon as opportunity offers. 



This mode of reproduction, we see, is altogether that 

 of an Alga. Pythium, though a Fungus, is not thoroughly 

 adapted for growth on dry land, for its normal reproduc- 

 tive processes can only go on under water. This is one 

 reason why seedlings attacked by Pythium are said to 

 damp off, for it is when they are kept too damp that 

 their enemy is best able to attack them ; the moisture 

 enables the Pythium to spread. This method of propa- 

 gation by zoospores allows of an enormously rapid 

 multiplication under favourable conditions ; its success, 

 however, is entirely dependent on the presence of 

 water. It is true that only a little water is necessary, 

 but still Pythium is entirely powerless to propagate its 



