THE MOLDS 



241 



minute globules of a fatty nature. The bread mold is an excel- 

 lent example of a saprophytic fungus. The hyphse grow all 

 through the porous substance of the moist bread and absorb 

 fluids containing products of the bread's incipient decay. The 

 material over which a saprophytic fungus grows and upon 

 which it lives is called its substratum. 



The fructifications of the bread mold are very characteristic. 

 Numerous erect branches arise, several in a group, from creeping 

 hyphse that develop clusters of short, root-like filaments at these 

 points (Fig. 211). The end of each erect branch then gradually 



FIG. 211. Growth habit of the bread mold (Rhizopus nigricans) 



Sketch showing two groups of erect hyphse bearing sporangia, with root-like 

 clusters of filaments at their bases 



enlarges and becomes separated from the stalk below by a dome- 

 shaped cross wall called the columella (Fig. 212, A). The ter- 

 minal cell becomes a spore case, or sporangium, and develops a 

 multitude of smoke-colored spores, which make the spore cases 

 appear as black heads upon the upright stalks (Fig. 212, B). 

 The spores are distributed by the breaking of the sporangium 

 wall, exposing the dome-shaped columella which remains at the 

 end of the stalks after the dispersal of the spores (Fig. 212, D). 

 The molds have a remarkable method of sexual reproduction, 

 which is, however, rarely found in the bread mold (Mhizopus), 



