214 PRACTICAL BOTANY 



one organism is held by the other in a condition of slavery. 

 In case of some dependent plants it is not easy to determine 

 the nature of their dependency. 1 



199. Bread mold (Rhizopus nigricans). If a piece of slightly 

 moistened bread is placed in a glass jar or covered in a dish 

 for a few days, an abundant supply of mold soon appears upon 

 it. There may even be several kinds of molds developed upon 

 the bread under such conditions within a very few days. The 

 common bread mold, or black mold, is the one which usually 

 appears. It grows about our homes in great abundance, soon 

 appearing when bread, fruits, and other favorable nutrient 

 substances are left exposed. When young the mold is white, 

 only assuming its blackish appearance when spores are formed. 



200. Bread mold : vegetative structures. A mass of growing 

 bread mold is composed of many white threads greatly entangled 

 one with another. This entanglement is due to the forward 

 growth of the many free ends of these threads. Each thread is 

 called a hypha (meaning "a single web"), and the whole net- 

 work of hyphce is the mycelium, or fungus mass. The mycelium 

 is the interwoven network of which one hypha is a single thread. 



Careful examination also shows that some of the hyphse 

 have grown down into the nutritive substratum (supporting 

 substance), 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 the bread. Branching downward from some of 

 the superficial hyphas are special root-like hyphse (rhizoids) 

 (Fig. 176), which descend and spread out within the nutrient 

 material. At such places upright hyphae also are formed. 

 From these areas 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 be formed. This 

 method of vegetative extension gave rise to a much-used name, 

 Mucor stolonifer, meaning " the stolon-bearing mold." 



1 Dependent plants are treated more fully in a separate chapter, but plant 

 dependency necessarily receives attention throughout ttus, discussion of the 

 fungi. 



