56 COMMON BLACK MOLD. 



LABORATORY WORK. 



GROSS STRUCTURE. 



The vegetative body of the plant consists of a network of 

 branches (mycelium) upon and within the material which 

 furnishes food, and upright branches from the mycelium. A 

 separate branch (hypJia) may pass through the substratum 

 and then emerge upon its surface as an aerial stalk. Observe: 



1. The general appearance of the entire mass of plants. 



2. The different positions of the threads with reference to 

 the supporting substance. 



3. Certain hyphae which arise from the mycelium and again 

 come in contact with the substratum, branching at the 

 place of contact, and thus extend the plant. 



4. The aerial hyphae (sporangiophores) upon which the black 

 tips (sporangia) have formed. 



MINUTE STRUCTURE. 



I. NUTRITIVE STRUCTURES. 



Carefully remove a small amount of the material from its 

 substratum, mount and study, observing: 



1. The network of hyphae composing the mycelium. 



2. The branching of hyphae. 



3. Absence of walls separating individual cells; therefore it 

 is a coenocyte. 



of the same subject by the same author in the Proc. Am. Acad. of Arts 

 ami Sciences, 40: 205-319, 1904, it is concluded that zygospore forma- 

 tion in the Mucorineae " is conditioned by the inherent nature of the 

 individual species and only secondarily or not at all by external fac- 

 tors." It is further concluded that there are two races of Rhizopus 

 nigricans (Mucor stolvnifcr), as well as of other Mucorinese. One race 

 is monoecious, the other dioecious. In order to obtain zygospores from 

 the dioecious race it is necessary to have both positive and negative 

 strains growing together. 



