FOOD-GETTING AND DIFFERENTIATION 105 



of energy which is transformed from the stored-up energy in 

 proteins and other foods, which in turn is derived from the 

 energy of foods obtained from other animals or plants, where in 

 turn it is obtained from other foods, until finally this energy is 

 traced back to the green plants. Green plants, in turn, get 

 their energy from the sun. A necessary step, therefore, in the 

 biology of animals is to trace out as far as possible the transfor- 

 mation of solar energy into that of protoplasm. The initial 

 steps in the process are connected with the structures and func- 

 tions of plants, and enough of these will be described to pave the 

 way for a clear understanding of the w r ork which the plants do 

 in nature. 



The lines of development of the two great kingdoms are 

 widely different. While at bottom the vital activities of plants 

 and animals are the same, the structural differentiations have 

 followed lines of entirely different requirements. The activities 

 of animals have been directed toward food getting and food 

 digestion and protection against enemies who would make food 

 of them, functions involving highly developed muscular sys- 

 tems, closely correlated nervous responses and centralized 

 nervous systems, and complicated organs for the digestion of 

 many different kinds of food. Their metabolism, therefore, 

 involves active destructive processes and the formation of 

 excessive waste matters, for the disposal of which complicated 

 excretory organs have been evolved. Higher plants, on the 

 other hand, are stationary; their food material being everywhere 

 about them, locomotor organs are not developed and their 

 nervous response is limited to protoplasmic irritability; waste 

 matters are relatively unimportant and easily disposed of, re- 

 quiring no complicated excretory organs. Their plan of de- 

 velopment, like that of animals, has been essentially in the 

 service of nutrition. Great trunks and branches have been 

 evolved, apparently in response to the need of presenting maxi- 

 mum chlorophyll-bearing leafy surfaces to the air and light, 

 while great subterranean roots absorb water and salts from the 

 earth. Strong frameworks of lifeless wood, giving resistance to 

 winds and weather, have been evolved for the support of the 



