DEVELOPMENT OF PLANTS 



227 



thick-walled gametospore (Fig. 136, B, C). After a resting 

 period, this gametospore grows directly into a new mycelium. 

 In some of the black moulds Blakeslee has made known that 

 reproduction is only effected by the union of hyphae from 

 diiiferent plants which must differ therefore in their nature, just 

 as you found to be the case in some species of Spirogyra. 



81. A Fly Fungus. — An interesting form allied to the mucors 

 is seen in the parasitic fungus Empusa, that produces an epi- 



FiG. 137. A fungus, Empusa, parasitic upon flies: A, fly surrounded by 

 a mass of discharged sporangia. B, enlarged view of several hyphae, showing 

 the discharge of the sporangia which are surrounded by a mucilaginous sub- 

 stance. — After Brefeld. 



demic among flies at certain seasons when they may be seen dead 

 and clinging to the woodwork and window panes surrounded by 

 a white halo (Fig. 137, A). This appearance is caused by the 

 discharge of numerous white sporangia that are found at the 

 ends of the hyphae that project from all sides of the fly's body 

 (Fig. 137, B). If, by chance, a fly should come within range 



