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. 
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 thus formed swells up, becoming globular in shape and its proto¬ 
plasmic contents 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 
