198 PHARMACEUTICAL BOTANY 
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. 
Rhizopus reproduces by two methods. The most common one is 
that of internal cell formation. In this asexual method a transverse 
wall is laid downm the sporangiophore near its tip. The terminal cell 
thus formed swells up, becoming globular in shape and its protoplas- 
mic 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 wall is 
