192 PLANT BIOLOGY 



(b) By preventing too rapid evaporation from the soil, 



through the help of the foliage. 



(c) By retarding the melting of snow, thus preventing 



freshets. 



(3) Value in affecting climate. 



(a) By bringing moisture into the air, which falls as 



rain. 

 (6) By setting oxygen free into the air in the process 



of starch making, 

 (c) By acting as a windbreak. 



(4) Economic value. 



(a) As a source of lumber and fuel. 



(6) As a source of food (nuts, maple sugar, etc.). 



(c) As a source of industrial raw materials (paper, 



tanning materials, wood alcohol, tar, pitch, 



turpentine, rosin, fibers). 



c. Dangers to forests. 



(1) Fires. (4) Careless lumbering. 



(2) Insects. (5) Fungi that cause disease. 



(3) Grazing of cattle. 



d. Results of deforestation. 



(1) Main cause of freshets, which cause destruction of 



property and loss of life ; they also fill up navi- 

 gable streams with soil and debris. 



(2) Drouth, with the consequent lessening of water power. 



(3) Timber famine, especially in hard woods. 



e. Methods used by the Government Bureau of Forestry to 



preserve forests. 



(1) Allow only the cutting of dead or mature trees. 



(2) Insist that each tree cut be replaced by another of the 



same kind. 



(3) Prevent the spread of fires. 



(4) Destroy insects that are injurious to trees. 



(5) Restrict cattle grazing to certain seasons. 

 3. Fungi and their relation to human welfare. 



a. Bacteria; microscopical appearance and size; reproduc- 



