202 REPRODUCTION OF A BLACK MOULD 



duct them to the female. For the same reason, the zoospores are 

 reduced to light motionless spores that are developed upon elon- 

 gated hyphae that expose them to the air currents for distribu- 

 tion. The ability of these spores, or sporangia, to produce 

 zoospores is doubtless the survival of a trait inherited from their 

 algal ancestors. 



80. Order c. Mucorales or Black Moulds. — These are among 

 the most common of the fungi and they are almost sure to appear 

 upon any cooked food or decaying matter that is exposed to the 

 air even for a very short time (Fig. 134). The mycelium has 



Fig. 134. Habit of growth of the black mould, Rhisopus: s, sporangia; 

 r, absorbing branches of the mycelium. 



practically the same structure as noted in the preceding groups. 

 but the black mounds have lost all motile reproductive bodies and 

 their relationship to any group of the algae is not known. Some 

 of the hyphae of the mycelium creep over the food supply and 

 send into it short branches which serve as organs of absorption, 

 while other rather thicker hyphae grow away from the mycelium 

 and reach up into the air (Fig. 134). The tips of these erect 

 hyphae are cut off by a transverse wall and enlarge into spherical 

 sporangia (Fig. 135). The protoplasmic contents of the sporan- 

 gia divides into a large number of small bodies or spores, each 

 of which contains a nucleus and becomes covered with a rather 

 thick smoky black wall. The numerous sporangia filled with 

 dark spores are the principal cause of the black color of these 

 fungi. While the sporangium is forming, the transverse wall 

 which separates it from the hypha, becomes convex, owing to the 



