188 APPLIED BIOLOGY 



that forest planting and forest conservation be practiced ex- 

 tensively. And not only is it important that forests should 

 be preserved and new ones developed for the sake of a con- 

 tinued supply of lumber; but, also, among many other things 

 which make forests valuable are their effect upon climate, 

 prevention of soil erosion, prevention of sudden floods, 

 aesthetic value, and affording protection for birds and other 

 desirable animals. Each of these is important enough to 

 warrant much attention to forestry ; and recognition of such 

 facts is responsible for the general awakening of interest in 

 preservation and improvement of American forests. The 

 United States government now maintains at Washington 

 a bureau, known as the Forest Service, which has charge of 

 the national forest reserves, and which also encourages private 

 work in forestry by publishing pamphlets and by giving 

 advice. Among the best of such pamphlets now available 

 are the " Primer of Forestry " by Pinchot, which is in two 

 parts (free to those who apply to the Department of Agri- 

 culture) ; and many leaflets (also free) giving information 

 as to how to plant special kinds of trees. The " Primer of 

 Forestry " should be obtained and read by all students of 

 biology. Another interesting book in the same line is Roth's 

 "First Book of Forestry." 



LEAVES OF SEED-PLANTS 



181. Functions of Leaves. In connection with the study 

 of the bean plant three functions of leaves (breathing, trans- 

 piration, and starch-making) have been mentioned; In 

 addition to these functions, which belong to all typical leaves, 

 some plants have leaves fitted for special functions, which will 

 be described in the paragraph on adaptations of leaves. 



In order to carry on most efficiently the three main func- 

 tions, it is important that leaves should be arranged so as to 

 have the most favorable exposure to light and air. This 



