LEAVES AND THEIR FUNCTIONS 141 



on the pitcher lead the insect to its destruction. The insect slips into the 

 fluid in the pitcher, is digested, and the proteid portion absorbed. 



Leaves as Food. — Some leaves are used directly by man for 

 food. Examples are cabbage, lettuce, Swiss chard, kale, broccoli, 

 and many others. These leaves contain (with a large percentage 

 of water) gluten (a proteid), starch, oil, and mineral matter. 

 These foods, properly admixed with certain fleshy foods, are of 

 great importance in giving a balance to diet. 



Economic Use of Leaves. — The practical use of green plants 

 to man is very great. Plants give off oxygen in the sunlight and 

 use carbon dioxide, which is given off by animals in the breath. 

 Thus parks containing green trees are truly the breathing places 

 of the city. 



Another very important use to man is seen in the fact that 

 leaves, falling to the ground, help to form a rich covering of 

 humus, which acts as a coat to hold in moisture. The forests are 

 our greatest source of water supply. The cutting away of the 

 forest always means a depletion of the reserv^e water stored in 

 soil; with consequent floods and droughts in alternation. 



Reference Books 

 for the pupil 



Andrews, Botany All the Year Round, pages 46-62. American Book Company. 



Leavitt, Outlines of Botany. American Book Compan3\ 



Dana, Plants and their Children, pages 135-185. American Book Company. 



FOR THE TEACHER 



Gray, Structural Botany, pages 85-131. American Book Company. 



Goodale, Physiological Botany, pages 337-353 and 409-424. American Book Com- 

 pany. 



Darwin, Insectivorous Plants. D. Appleton and Company. 



Green. Vegetable Physiology. J. and A. Churchill. 



Lubbock, Flowers, Fruits, and Leaves, Last Part. The Macmillan Company. 



MacDougal, Practical Text-hook of Plant Physiology. Longmans, Green, and Com- 

 pany. 



Report of the Division of Forestry, U.S. Department of Agriculture, 1899. 



Strasburger, Noll, Schenck, and Schimper. A Text-hook of Botany. The Mac- 

 millan Company. 



