236 INTRODUCTION TO BOTANY 



usually appears. It grows in and about our homes in great 

 abundance, upon bread, fruits, and other favorable nutrient sub- 

 stances that are left exposed. When young the mold is white, 

 only assuming its blackish appearance when spores are formed. 

 223. Vegetative structures, and nutrition of bread mold. A 

 mass of growing bread mold is composed of many white 

 threads grown together until they have become closely inter- 

 woven. Each thread is called a hypTia ("a single web "), and 

 the whole network of hyphse is the mycelium, or fungus mass. 



FIG. 184. Bread mold 



At the left is a slightly magnified illustration of plants, one of which has given 

 rise to the other by means of a runner, or stolon. Descending are the rhizoids and 

 ascending are the aerial branches, upon the tips of which spores are borne within 

 sporangia. At the right a more highly magnified sporangium is shown. Its wall 

 (to) incloses many spores (s) , through which may be seen the columella (c) , which 

 is the swollen tip of the stalk upon which the sporangium is borne. This wall may 

 be broken away, so as to leave some of the spores lying upon the columella, as is 

 seen in two cases of the plants shown at the left 



Careful examination also shows that some of the hyphee 

 have grown down into the bread, and if one could see through 

 the bread after mold has grown on it for a few days, much 

 of the mycelium would be seen within it. Branching down- 

 ward from some of the superficial hyphse are special root-like 

 hyphse (rhizoids') (fig. 184), which descend and spread within 

 the nutrient material. At such places upright hyphse also 

 are formed. Long, runner-like branches (stolons') may extend 

 over the surface a little way. From the stolons a new set of 

 rhizoids and upright hyphae may grow. 



