214 DISTRIBUTION OF THE BLACK MOULDS 



ture in the sporangium relaxes, owing to the loss of its watery 

 contents, and assumes an umbrella shape, as seen in Fig. 135, F. 

 You can readily understand why these black moulds are so com- 

 mon by counting the number of sporangia on a small bit of myce- 

 lium and then estimating the number of spores in a sporangium. 

 So numerous and light are the spores that they are carried every- 



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. 



where. It is only necessary to expose a bit of moist bread for a 

 few moments to the air and then enclose it in a damp chamber to 

 secure a luxuriant crop of these plants. Under certain conditions 

 the sexual method of reproduction is effected by the union of 

 two club-shaped hyphae, as shown in Fig. 136, A. As these 

 hyphae meet, the tip of each branch is cut off by a wall and the 

 contents of the two tips fuse, forming a thick-walled gametospore 



