GRASSES OF IOWA, 



115 



This contains the asci. Each ascus is surrounded by a delicate 

 wall and contains eight biconvex ascospores. 



Rhizopus nigricans. Ehrh. — The third mould commonly found 

 is the black mould. The mycelium spreads over the tissue, and 

 on the surface small black bodies, the sporangia, are produced. 

 The conidiophore arises from the felted mycelium. The con- 

 idiophore bears an enlarged spherical head, the sporangium, 

 within which occur the spores. On adding water to the speci- 

 men, the wall of the sporangium collapses and the end of the 

 stalk, known as the columella, turns back, giving it something 



Fig. 64. (1) Common black mould (R/ifooptts nigricans) showing sporangia and 

 method of spreadlrg by stolons. (3) R. nigricans showing rhizoids, conidiophore, colu- 

 mella, sporangium and spore. (3) Zygospores ot one of the mucoraceae showing method 

 of conjugation. 



of the appearance of an umbrella. The columella before it 

 collapses projects into the sporangium. The spores germinate 

 readily when placed in a moist atmosphere. In addition to the 

 production of a sporangium a stalk may bend over and cause 

 the further extension of the fungus by producing what is 



