THE FUNGI 



545 



[Chap. XLIV 



more than the digestion and oxidation of organic substances. Growth of 

 the fungus may continue until the food is exhausted. 



The mycehum starts from a spore as a single hypha and spreads over 

 the bread by terminal growth of its multitudinous branches. At node-like 

 points on the spreading hyphae upright branches and several rhizoids 

 develop. These nodes also become new centers from which radiating 

 horizontal hyphae extend and increase the complexity and density of 

 the mycelium. 



The tips of the upright hyphae enlarge and foim globular spore cases, 

 sporangia, which eventually contain many small round spores (Fig. 236). 



Fig. 236. Bread mold {Rhizopus): A, general habit of growth and reproduction 

 by asexually formed spores; B, C, D, E, and F, stages in the fusion of hyphae of 

 male and female mycelia and the formation of a zygote. 



Many sporangia are usually produced about the same time, and upon 

 their rupture millions of black spores are liberated from them. The 

 spores are so light that they float in the air for long periods; hence it is 

 easy to see whv moist bread when exposed to the air for even a short 

 time and then placed in a closed container soon becomes "moldy." When 

 spores come to rest on a moist organic substrate, they germinate almost 

 immediately, and from them new mycelia originate. When bread is 



