THE USEFUL MICROBES 
49 
Most molds, when they first begin to grow, 
are soft, fluffy, white masses, but later they 
may become blue, green, brown, black, or red. 
If we look at a mold under the microscope, we 
see that it is a dense mass of fine white threads. 
The different kinds vary in the fineness of the 
thread, the speed with which they grow, and 
in the color they later take on. These threads, 
by their growth, work into the depths of the 
matter upon which they are growing. If they 
are on the surface of bread, the fine fibers push 
their way into the loaf. When growing on 
any soft food, the mold threads, which are seen 
on the surface, really extend into the substance 
for some distance, although they are so small 
and transparent that we cannot see them. 
Molds grow on almost all food-stuffs; they 
can also live, though less easily, on woolen or 
cotton cloth, or even on leather. Wheat-flour, 
bread, and cake, are sure to grow mold if left 
in a warm, damp place. Cheese is one of the 
very best foods for mold. That is why cheese 
so easily gets moldy. When molds appear on 
Mold is a small plant which is some¬ 
times useful and sometimes harmful 
What are 
molds lit{e? 
