FUNGI, BLACK MOLD 



277 



and others into the air if the air is moist. The mycelium is con- 

 tinuous, i.e., it is not divided up into cells by cross walls. The 

 protoplasm is coarsely granular and shows numerous vacuoles of 

 varying size (fig. 221). The protoplasm shows streaming move- 

 ments. It flows along in a thread-like stream, or in other cases 

 there may be smaller currents up and down the thread. There 

 are large numbers of nuclei in the protoplasm, but they cannot 

 be demonstrated without careful treatment according to certain 



Fig. 222. 



Rhizopus nigricans. Different stages in conjugation of + and strains to form zygospores. 



technical methods. Cross walls appear where reproductive 

 bodies or organs are formed, and rarely here and there in old 

 mycelia. 



418. Sexual reproduction. Sexual reproduction takes place 

 by conjugation. This occurs between two threads or branches of 

 mycelium which are of an opposite sex nature. One cannot dis- 

 tinguish between male and female according to the size and 

 appearance of the conjugating branch, though sometimes at 

 a later stage one becomes much larger than the other. The 

 branches meet at their ends, and each swells into a club-shaped 



