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 hypha (“a single web”), and 
the whole network of hyphee is the wycelium, or fungus mass. 
Fie. 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 aérial branches, upon the tips of which spores are borne within 
sporangia. At the right a more highly magnified sporangium is shown. Its wall 
(w) incloses many spores (s), through which may be seen the columella (¢), 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 hyphe 
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 hyphe are special root-like 
hyphe (rhizoids) (fig. 18+), which descend and spread within 
the nutrient material. At such places upright hyphe 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 hyphe may grow. 
