TAXONOMY 249 



bears upon its summit a spheroidal sporangium containing numerous 

 small brownish multinucleate spores called endospores. The wall 

 of the sporangium is beset with asperites of calcium oxalate. Spring- 

 ing from the base of the sporangiophores or aerial hyphae one or more 

 stoloniferous hyphae traverse a portion of the surface of the sub- 

 stratum and their tips, coming in contact with the substratum, 

 swell up forming an adhesive organ or appressorium which branches 

 out below into a cluster of spreading submerged hyphae and above 

 into several aerial hyphae bearing sporangia. This method of 

 growth proceeds until the entire surface of the nutritive medium is 

 covered with a dense fluffy mycelium. 



D ;U 



If 



FIG. 124. Rhizopus nigricans. A, Young sporangium, showing columella 

 within; B, older sporangium, with the 'wall removed, showing ripe spores covering 

 the columella; C, D, views of the collapsed columella after dissemination of the 

 spores. (Gager.) 



Rhizopus reproduces by two methods. The most common one is 

 that of internal cell formation. In this asexual method a transverse 

 wall is laid down in the sporangiophore near its tip. The terminal 

 cell ftius formed swells up, becoming globular in shape and its proto- 

 plasmic ontents become changed to form numerous spores within 

 the wall of the sporangium or enlarged terminal cell of the sporangio- 

 phore. The partition wall, separating the lumen of the sporangium 

 from that of the sporangiophore, bulges into the sporangium as a 

 dome-shaped structure, which is termed the columella. Upon the 

 ripening of the spores the wall of the spore case bursts, liberating 

 them. These, falling upon moist nutrient substrata, germinate and 

 ultimately form new Rhizopus plants. Under certain conditions 

 Rhizopus reproduces sexually. Thicker and shorter club-shaped 

 hyphae arise on opposite branches of the mycelium. A partition 



