THE FUNGI 



261 



Nutrition. Rliizopus is able to grow not only upon bread but 

 upon a great variety of organic material if kept in moist places. 

 From some substances it is undoubtedly able to absorb foods 

 which are already in solution, while in other cases, as on breads, 

 much of the food material is insoluble and must first be digested 

 by the submerged hyphse before it can be absorbed and used 

 by the cells of the mold mycelium or by the sporangia during 

 spore formation (Fig. 140). In order to digest the food the sub- 

 merged hyphse secrete digestive ferments similar to those already 

 discussed under yeasts. These digestive ferments diffuse out of 

 the hyphse and con- 



Sporcs 

 * !" 



Columella' 



vert the starches, fats, 

 and proteins of the 

 bread on which the 

 mold is growing into 

 soluble and diffusi- 

 ble foods. In other 

 words, the mold di- 

 gests its food much 

 as higher plants do, 

 except that the di- 



,8pores 

 .Columella 



Spor 

 Mycelium, 



FIG. 140. A drawing illustrating the growth of 



Ehizopus on and within a piece of bread 

 gestioil in the mold The absorbing and fee ding mycelium, composed of 

 takes place entirely branched hyphse, is shown within the bread; also a 

 . . , f , , , -, stolon and two groups of sporangia 



outside of the body 



cells of the plant and within the nutrient medium immediately 

 surrounding its hyphse. Some of the black molds, in addition 

 to the digestive enzymes, are able to secrete enzymes which 

 bring about fermentations in sugar solutions exactly like those 

 of the yeast. 



Asexual reproduction. The hyphse which bear the sporangia 

 and spores in RJiizopus arise at the point of origin of the root- 

 like outgrowths which spring from the stolons, where they first 

 grow out as short, erect branches of the mycelium (Fig. 141). 

 These aerial hyphse soon begin to swell at the ends, producing 

 a light-colored spherical enlargement which is the beginning 

 of the future sporangium. The entire structure, including the 

 erect hypha and its swollen end, is now called a sporangiophore, 



