236 BIOLOGY 



oxygen, forming CO 2 and H 2 O, which pass off into the air or 

 sink into the soil, while the other ingredients are incorporated 

 with the substances of the soil to form food for the next genera- 

 tion of plants. 



The Fungi thus have the extremely important function of 

 bringing back into a primitive condition much of the material 

 manufactured by plants which otherwise could not readily be 

 disposed of. When we consider that bacteria are nature's 

 agents for decomposing proteids, that the yeasts act in a similar 

 way upon carbohydrates, and that the larger Fungi attack the 

 great mass of vegetable material which is otherwise beyond 

 the reach of animal life, we can see that the group of Fungi is 

 of immense significance in nature. They form a connecting 

 link between the products of one generation of plants and the 

 next. Without their agency, organic material proteids, fats, 

 starches, leaves, woods, etc. would accumulate, and in time 

 vegetation would cease, because the earth would be covered 

 with the remains of past generations, which would crowd life 

 out of existence. The Fungi thus act as scavengers, cleaning up 

 the surface of the earth and rendering nature's processes con- 

 tinuous by ever returning to the soil the ingredients upon which 

 subsequent generations can feed. 



The Food Cycle Complete. Thus, as the result of the action 

 of the Fungi and of animals, all of the surplus starch and sugar, 

 all the fat, proteids, wood, and cellulose, and indeed all other 

 materials which have been built up by the constructive processes 

 of plants, are eventually broken down, and in the end reach 

 a condition like that from which they started. Carbon dioxid 

 and water are produced, as well as nitrates and certain other 

 mineral salts. The carbon dioxid, being a gas, flies off into the 

 air to join the store of this gas in the atmosphere; the water 

 evaporates or sinks into the soil; and the nitrates and other 

 mineral ingredients also find their way into the soil. These 

 ingredients, again within reach of plant life, are seized by the 

 green plants and built up into a new generation of plants to 



