334 ELEMENTS OF GENEKAL SCIENCE 



medicinal oil. The lean meat of animals is particularly rich 

 in proteins, as the fatty parts are in fats, but flesh is poor 

 in carbohydrates. 



The enormous importance of the industries which are pro- 

 ducing these supplies these great quantities of stored plant 

 food can scarcely be overestimated. In times of peace as well 

 as in war the quantity and availability of this surplus food 

 is of greatest significance in determining a nation's welfare. 



338. Use of food by plants. If the stored food is not used 

 by men or removed in some other way, the plant will finally 

 use it in its processes of growth. When a seed sprouts, 

 for example, it is several days before the little plant pushes 

 through the ground and the chlorophyll is formed which 

 enables the plant to utilize the carbon dioxide of the air. 

 During this time the living material and the cell walls of 

 the stem and roots are made from the stored material in the 

 seed. We know that in the sprouting seed the reserve foods 

 are first made soluble and diffusible (digested) by the action 

 of enzymes, but the wonderful process by which these simple 

 substances become a part of the living material of the cells 

 (protoplasm) is still a mystery. The term " assimilation " is 

 used to cover the constructive process by which new cellular 

 material is made either from reserve material in a seed or 

 from materials manufactured by the plant in the processes of 

 photosynthesis and protein synthesis. The process of assimi- 

 lation is undoubtedly similar to the process in our own bodies 

 by which the food which is digested and carried by the blood 

 to the cells of the body becomes a part of the cell. 



339. Assimilation and respiration. It will be worth while 

 here to contrast assimilation and respiration. Assimilation is 

 a process by which more protoplasm is constantly made from 

 simple chemical compounds, and it is therefore a constructive 

 process. Respiration is a destructive process by which pro- 

 toplasm and compounds closely associated with it are de- 

 stroyed and the energy which they yield is made available. 



