COMPARISON OF ANIMAL AND PLANT BIOLOGY 123 



FIG. 41. Epidermis from leaf of onion bulb. 

 Seven cells are in various stages of division. 

 (From Wilson,) 



whose specialty is the study of cells are continually mak- 

 ing discoveries with the microscope which make still more 

 impressive the similarity of cells in animals and plants. 



In both animals and 

 plants the cells are 

 grouped to form tissues, 

 and the tissues to form 

 organs, which are simply 

 groups of cells for per- 

 forming a particular 

 work necessary in the 

 life of the living thing. 



112. Food of Animals 

 and Plants. Both re- 

 quire food containing 

 the elements found in 

 their bodies. That the necessary elements are the same is 

 evident from chemical analysis and from the fact that many 

 animals (the herbivorous) live on plants as food. Both ani- 

 mals and plants require foods* containing carbon, hydrogen, 

 and oxygen. Plants which have no chlorophyll, and all ani- 

 mals, must depend for such food upon the sugar, starch, and 

 oils which have been made from carbon dioxide and water by 

 green plants ( 99) . Herbivorous animals get carbohydrates 

 and oils directly by eating plants ; but carnivorous animals 

 get similar food from the fat, sugar, and other substances in 

 the flesh of herbivorous animals. Thus when a frog eats an 

 earthworm it gets materials which the worm got from its 

 plant food. In short, all animals, and plants like the mush- 

 rooms, depend upon those plants which are able to combine 

 the elements of carbon dioxide (C0 2 ) and water (H 2 0) to 

 form such foods as starch, sugar, and fat. 



In addition to foods containing only three elements (C,H,0), 

 animals and plants require foods containing also the element 

 nitrogen. Most plants are able to get nitrogen by using 



