CHAPTER IX 

 MUCORALES 



Mycelium profusely developed, filamentous, richly branched, 

 when young coenocytic, in age frequently provided with trans- 

 verse septa, terrestrial, usually saprophytic, in some species para- 

 sitic, consisting of nutritive hyphae buried in the substratum 

 and aerial hyphae on which the reproductive bodies are usually 

 borne; the aerial mycelium usually prominent, the group having 

 been designated in consequence the moulds; thick-walled, inter- 

 calary, globose to barrel-shaped chlamydospores, and thin-walled 

 oidia not infrequently formed on the mycelium (Lendner 1908 b: 

 Jigs. 16-18); sporangia borne on specialized sporangiophores, 

 sometimes accompanied by or replaced by few-spored sporangiola 

 or unicellular conidia; sexual reproduction accomplished by the 

 conjugation of similar gametangia (coenogametes), and resulting 

 in the formation of a thick-walled zygospore ; azygospores some- 

 times developed in the absence of the sexual fusion; zygospore 

 germinating by a germ tube which usually bears a single large 

 apical germ sporangium; swarmspores absent throughout the 

 group. 



In the lower members of the group asexual reproduction is 

 accomplished by means of sporangiospores borne in large, globose 

 to pyriform, many-spored sporangia. The septum which 

 delimits the sporangium is often strongly convex, and appears 

 as a more or less columnar protrusion of the sporangiophore 

 into the sporangium. This apparent protrusion, termed the 

 columella, usually remains in position after the sporangial wall 

 has disintegrated, and the spores are sometimes found adhering 

 to it. 



The columella does not result in fact from a bulging upward 

 into the sporangium of a transverse septum. It is formed in the 

 position in which it lies at maturity, and is laid down along a 

 prominent cleavage plane in the cytoplasm. Similar cleavage 

 planes run progressively in all directions, arising from the col- 

 umella, sporangial wall, and vacuoles, and finally cut the proto- 



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