I0 RELATIONS OF FUNGI 



organic substances already prepared for him. No animal is capable 

 of living on purely mineral food, and we have seen, on the other 

 hand, that in addition to their respiration, green plants an oak, a 

 rose, a moss, and even the microscopic green algae have the power 

 of decomposing the carbonic oxide of the air, and, with the elements 

 of water added, actually manufacture organic food. As we have 

 seen, this is the common function of green plants and at once 

 distinguishes them from animals on the one side, and fungi and 

 other colorless plants on the other. Fungi, like animals, require 

 organized food on which to live and they must, therefore, like 

 animals, depend on green plants to manufacture for them organic 

 food from the constituents of air and water and mineral salts. 

 The reasons why fungi are not animals, are the very important 

 ones, that in structure, in the chemical composition of their cell- 

 walls, and in their methods of reproduction the fungi are closely 

 related to the algae. 



Some 35,000 or 40,000 species are known at present of which 

 perhaps 8,000 are known to inhabit North America. They vary 

 in size from single microscopic cells to systems of entangled 

 threads many feet in extent which develop reproductive bodies 

 as large as a man's head, or even larger. In color they vary 

 from white through yellow, blue and red to black. Although 

 some of them are green they never possess chlorophyl, and this 

 one negative character is their chief distinguishing characteristic. 



The species of fungi, small as many of them are, are usually 

 well characterized, at least as well as the species of the higher 

 plants. Some of the difficulties that are experienced in recognizing 

 our species does not arise so much from the lack of inherent differ- 

 ences, but comes from the fact that there is much similarity be- 

 tween the fungous flora of Europe and America and many of 

 their species and some of ours were poorly defined at the begin- 

 ning, and many of the descriptions of the early writers are difficult 

 to interpret, and to assign to existing forms. There are other diffi- 

 culties of an entirely different character to which we will allude 

 later. We are sometimes accustomed to group fungi as parasitic 

 when they draw their sustenance from other living organisms, 

 and saprophytic when they live on decaying matter, but there are 

 various grades intermediate between these artificial groups. It 

 will be convenient for our purpose, however, to refer to them in 

 this way. 



