146 I^IVING PLANTS 



It is literally true that the existence of every 

 living thing is ultimately dependent upon the 

 activity of plant-green. 



The actual conditions are as follows: the 

 elements which enter into the construction of 

 protoplasm are carbon, nitrogen, oxygen, hy- 

 drogen and phosphorus. These elements are 

 found in the form of free gases or simple com- 

 pounds in the soil and atmosphere, and can- 

 not be used by protoplasm until built up into 

 the form of complex compounds. The con- 

 struction of compounds indispensable for the 

 nutrition of plants and animals does not re- 

 Importance of suit from mere proximity of the elements, 

 chlorophyll since those most highly desirable are chem- 

 ically inactive to one another, and wnll unite 

 only under the influence of energy from with- 

 out. The substances are selected and ab- 

 sorbed in their elemental condition by the 

 plants, and in the crucible of the cell, glowing 

 with potentiality absorbed from sunlight, are 

 fused together and made ready for assimila- 

 tion by protoplasm. 



The most important synthetic process is 

 that which results in the formation of carbon 

 hydrates from carbon dioxide and water. If 

 this process were carried on by means of en- 

 ergy furnished by the activity of the proto- 

 plasm, the expenditure entailed would over- 

 balance the benefits gained by the assimilation 



