THE FUNGI : ARCHIMYCETES AND PHVCOMYCETES 217 



Since it is very rare to find any oospheres lying among mature oospores it 

 seems likely that those which fail to be fertilized develop parthenogenetically. 

 In any case it is well known that in many species antheridia are either only 

 rarely developed or not at all. In such instances, parthenogenetic develop- 

 ment of the oospheres appears to be the rule. The oospore germinates by the 

 formation of a germ tube which eventually produces fresh zoosporangia. 



With one or two exceptions all the species of Saprolegnia are saprophytes 

 on dead organic material, but Saprolegnia parasitica lives as a parasite on the 

 gills offish, causing the well-known Salmon Disease. This disease frequently 

 attacks goldfish kept under unfavourable conditions in small tanks. It has 

 been recently shown that excess of Calcium in the water favours the develop- 

 ment of the fungus and makes the fish more liable to attack. 



Oospore 



Zoospore 

 (Epical flagelta 



Fertilization 

 Tube 



ndium 



Saprolegnia Plar 

 Fig. 208. — Life-cycle oi Saprolegnia. 



Monoblepharidales 



The Monoblepharidales are saprophytic Phycomycetes which live sub- 

 merged in fresh water on undecorticated twigs. The hyphae are filamentous 

 and coenocytic. The protoplasm forms an extremely regular network which 

 makes them easily recognizable. Rhizoids pass into the substrate upon which 

 the Fungi live, and through them food material is presumably absorbed. The 

 vegetative mycelium is sparsely branched, is rigid and possesses no septa, 

 except in relation to the reproductive organs. 



Asexual reproduction is by zoospores produced in filamentous terminal 

 zoosporangia. The zoospores possess a single posterior flagellum. Sexual 

 reproduction is oogamous. The antheridia produce motile antherozoids 

 with a single posterior flagellum. The oogonium produces a single oosphere 

 which is non-motile. The result of fertilization is a thick-walled, golden- 

 brown oospore. 



The order is a small one with a single family, the Alonoblepharidaceae, 

 which contains only one important genus, Monoblepharis. 

 8a 



