PLANTS IN THEIR RELATION TO HUMAN WELFARE 139 



foreign countries, notably in Germany, the forests are so 

 used that year after year they supply the requisite timber, 

 and still continue to do their much needed work in conserv- 

 ing the rainfall. Such must be the policy in our country 

 if we wish to escape most disastrous penalties that always 

 result from forest destruction. 



Another method of forest protection is that afforded by 

 cutting trees in such a way as to form long, treeless strips of 

 land known as fire lanes. Systems of telegraphic communi- 

 cation from one part of the forest reserves to another and fire 

 wardens are necessary factors in efficient protection of forests. 



III. FUNGI AND THEIR RELATION TO HUMAN WELFARE 



146. Fungi. Thus far we have confined our attention to 

 plants which are easily visible to the naked eye and which 

 consist of roots, stems, and leaves. While we ordinarily 

 think of these as the common plants, in reality the most 

 common plant organisms are those which have neither roots, 

 stems, nor leaves, and which in many cases are microscopic 

 in size. The smallest and most numerous of these are known 

 as bacteria, which are found all about us, in the soil, in the air 

 we breathe, on the food we eat, and in the water we drink. 

 Bacteria belong to a great group of plants called fungi. 

 All fungi are characterized by the absence of chlorophyll, 

 hence plants' of this group cannot manufacture their carbo- 

 hydrate food out of materials from the soil and air, -but are 

 dependent on foods made by green plants. More familiar 

 to us, perhaps, than bacteria are the fungi known as mush- 

 rooms and toadstools, and the molds and mildews. Still 

 other fungi are the yeasts, the rusts, and the smuts. Because 

 of the enormous economic importance of many of these forms, 

 we shall consider more or less in detail the structure, func- 

 tions, and life-history of several of them, 



