THE SOURCE ANb NATURE OF VITAL ENERGY 301 



arising from the destruction of that portion of the starch which 

 was utilized as a source of energy for the constructive processes. 

 The carbon dioxid and water are waste products and are liber- 

 ated at once by the process of excretion. 



Thus it will be seen that there are two processes going on 

 in a plant body. One photosynthesis is a constructive 

 process by which the sun's energy is stored; the other metas- 

 tasis is a destructive process by which the energy is liber- 

 ated. The former process is going on in green leaves and only 

 in sunlight; the latter takes place in all of the living parts of 

 the plant, whether in sunlight or in darkness, at all times when 

 the plant is carrying on its life processes. By the former 

 process starch is being made; by the latter the plant manu- 

 factures a host of materials which are stored away in its body 

 in the form of proteids, wood, fat, cellulose, or other substances. 



Plants Produce an Excess of Organic Material. In all gre^n 

 plants, photosynthesis is much in excess of the metastasis, and 

 green plants are constantly manufacturing a quantity of starch 

 and other organic products, far more than they need for their 

 own use. 



The materials thus produced serve not only as a reserve 

 for their own future use but also for most other forms of ac- 

 tivity on the earth. All fuel which is used by our numerous 

 engines, whether wood, coal, oil, or gas, can be traced back to 

 plant life, and represents, therefore, the sun's energy stored 

 by photosynthesis. The food of all animals also comes from 

 plants. 



THE LIFE OF AN ANIMAL 



Stored Energy Utilized by Animals. The only source of 

 energy available for animals and colorless plants is that stored 

 up by green plants, and rendered available when liberated by 

 the destruction of the compounds that hold it. The general 

 result of animal life is a destructive one, with its resulting 

 liberation of potential energy. Animal protoplasm is, however, 

 able to carry on some constructive work. It can make fats 



