THE GENERAL NATURE OF MOLDS 17 



can growthrough food material will depend upon the tough- 

 ness or firmness of the material. Upon damp leather the 

 thread is not capable of growing underneath the surface 

 so readily as it can upon bread. This thread is known to 

 botanists by the term mycelium, and by this term we shall 

 hereafter refer to it. The young mold is a white, loose 

 mass of mycelium, but as it grows older it becomes denser 

 by continued branching of the thread. 



Fruit. After a while (usually two or three days' growth) 

 the surface of the mold begins to show some color, — 

 either blue, brown, red, or some other color. The appear- 

 ance of the color on the surface indicates that the plant 

 is fruiting, i.e. producing spores or reproductive bodies. 

 The spores of different species of mold are produced in 

 quite different ways, and botanists classify molds by their 

 methods of forming fruit. It will not be necessary for us 

 to consider more than one or two of them. 



In the common blue mold the spores are produced as 

 follows. After the mycelium has grown for some time 

 there arise from its surface tiny threads growing vertically 

 into the air. These threads, after extending for a very 

 short distance, divide into little branches (as shown in 

 Fig. 5, c), several branches arising from a single stem. 

 After these branches have grown for a short distance 

 they begin to be divided by slight constrictions, like rings, 

 around them, so that each one of them looks like a string 

 of beads (Fig. 5, c). These rings cut deeper and deeper 

 into the branch until finally it is broken up into a string 

 of a dozen or more small round balls (Fig. 6). These 

 little balls (Fig. 6) are the spores. When seen under the 

 microscope they appear quite transparent, but when a 



