BLACK MOLD 49 



separated by a thin wall or columella, which arches upward, 

 thus forcing the nuclei and protoplasm to the outer part of 

 the sporangium. At this time the central part of the sporan- 

 gium and the hyphse do not contain any nuclei. The nuclei 

 in the sporangium separate into groups of six or more. 

 Finally each nucleus becomes surrounded with protoplasm 

 and a thin cellulose wall to form a spore. When the spores 

 are all formed, the outer wall of the sporangium breaks open 

 and the innumerable spores float away on the air currents. 

 Each spore under favorable conditions develops into a black 

 mold. 



Vegetative Reproduction. Frequently an aerial hypha will 

 grow down into the substrata, branch into numerous sub- 

 terranean and aerial hyphae and develop a typical plant, 

 which may reproduce in the same way. 



Sexual Reproduction (by Conjugation). It has only recently 

 been discovered that there are two types of black mold 

 plants; namely, male and female. From each of these plants 

 lateral branches develop which grow toward each other until 

 their tips meet. The tips enlarge and become separated 

 from the hyphse by a wall. The contents of the two tips 

 fuse to form the zygospore, which develops a thick black wall. 



Germination of the Zygospore. The zygospore upon germi- 

 nation develops directly into an aerial hypha which forms a 

 sporangium containing typical spores. Rhizopus does not 

 possess chlorophyll; therefore, it must obtain its food from 

 decaying organic substances. Rhizopus and all similar 

 plants are called saprophytes. In canning fruits and vege- 

 tables great care must be taken to kill the spores of molds 

 and to keep the cans air-tight; otherwise their contents will 

 become moldy and unfit for use. 



