WHAT ARE MICROORGANISMS? 



in many cases, by growing, to force its way into the solid mass 

 of hard substances, like wood, and to push itself between the wood 

 fibers. Thus it is a primary agent in effecting the destruction of 

 wood. Such a mass of branching threads is called a mycelium, and 



FIG. i. One of the higher fungi, the common bread mold, Penicillium glaucum. 

 a, the whole plant; b, one of the spore-bearing branches more highly magnified. 



is found in all the Fungi of this class. So far as the mycelium is 

 concerned, most of these plants are much alike. But the different 

 species have many different methods of reproduction, and it is 

 chiefly upon their reproductive bodies that botanists rely to distin- 



FIG. 2. Mucor, a common mold, 

 showing mycelium and spore for- 

 mation. 



FIG. 3. Aspergillus, a common mold, show- 

 ing mycelium and spore formation. 



guish the different species. After the mycelium has grown for a little 

 time, it commonly sends up into the air small or large branches that 

 produce spores, or reproductive bodies. The method of spore 

 production differs sufficiently in the different fungi to make it 



