FUNGI: MUCOR, 



179 



rangium becomes dissolved, except a small collar around the 

 stalk which remains attached below the columella (fig. 192). 



Fig. 191. 



Group of sporangia of a mucor (Rhizopus nigricans) showing rhizoids and the stolon extend- 

 ing from an older group. 



By this means the gonidia are freed. These gonidia germinate 

 and produce the mycelium again. 



389. Sexual stage. This stage is not so frequently found, but may some- 

 times be obtained by growing the fungus on bread. 



Conjugation takes place in this way. Two threads of the mycelium which 

 lie near each other put out each a short branch which is clavate in form. 

 The ends of these branches meet, and in each a septum is formed which cuts 

 off a portion of the protoplasm in the end from that of the rest of the my- 

 celium. The meeting walls of the branches now dissolve and the protoplasm 

 of each gamete fuses into one mass. A thick wall is now formed around this 

 mass, and the outer layer becomes rough and brown. This is the zygote or 

 zygospore. The mycelium dies and it becomes free often with the suspensors, 

 as the stalks of these sexual branches are called, still attached. This zygo- 

 spore passes through a period of rest, when with the entrance of favorable 

 conditions of growth it germinates, and usually produces directly a sporan- 

 gium with gonidia. This completes the normal life cycle of the plant. 



390. Gemmae. Gcmmas, as they are sometimes called, are often formed on 

 the mycelium. A short cell with a stout wall is formed on the side of a 



