CONTENTS ix 



PAET V. LIFE UPON THE EAETH 



PAGE 



CHAPTER XXIII. THE PLANT COVERING OF THE EARTH 227 



Abundance of plants. Variety among plant formations. Value of 

 wild plants. Cultivated plants. 



CHAPTER XXIV. ABSORPTION FROM THE SOIL BY PLANTS 234 

 The problem. Loss of water from the soil. Osmosis. Root struc- 

 ture. Root surface. Water-carrying tissues. Solids absorbed only 

 when in solution. Root surface and transplanting. Summary. 



CHAPTER XXV. THE WORLD'S FOOD SUPPLY 241 



The demand for food. The source of food. Composition of foods. 

 Protein manufacture. Loss of nitrogen from soil. The supply of 

 nitrogen. The value of the soil. Summary. 



CHAPTER XXVI. UTILIZATION OF FOOD IN THE PLANT . 246 



Need of food in the plant. Where food is used. The method of 

 transfer. Digestion of starch. Digestion of other substances. 

 Transference in the plant. Food storage. Use of food by plants. 

 Assimilation and respiration. 



CHAPTER XXVII. NUTRITION OF ANIMALS 253 



Plants and animals. Processes of animal nutrition. Mastica- 

 tion : teeth. Structure of the teeth. Mastication : the saliva. 

 Mastication : use of the saliva. Digestion in the stomach and 

 intestines. Circulation. The heart as a force pump. Transporta- 

 tion and assimilation of food. Respiration. Proper nutrition. 



CHAPTER XXVIII. HYGIENIC ASPECTS OF NUTRITION . . 262 

 The purpose of food. The body a machine. Prolonged mastica- 

 tion. Heavy eating. Variety of food. Contaminated food. Food 

 and filth. Circulation and nutrition. Breathing and nutrition. 



CHAPTER XXIX. REPRODUCTION IN PLANTS AND ANIMALS 270 



Meaning of reproduction. Reproduction of the yeast plant. 

 Reproduction of pond scum. The frog's egg. Development of the 

 egg. The tadpole. Reproduction in birds and mammals. Repro- 

 duction in seed plants : the flower. The pistil. The stamen. The 

 embryo plant. The seedling. Vegetative reproduction. 



