LEAVES IN SEASONS 147 



of the substances formed. It is clearly ap- 

 parent, therefore, that the organism must 

 receive energ\^ from some external source and 

 must be able to convert this energy into the 

 forms necessary to promote chemical synthe- 

 sis. Sunlight is a universal source of energy 

 and green plants are the only organism capa- 

 ble of converting its rays into available ener- 

 gy. The transformation is effected by means 

 of chlorophyll. 



It is true that a few lower forms, inclusive 

 of the "sulphur" and '4ron" bacteria among 

 plants and some of the lower forms among 

 animals, are able to accomplish the construc- 

 tion of carbohydrates, but the total result 

 of their activity is indefinitely unimportant, 

 and is doubtless at the cost of energy furnish- 

 ed by complex compounds derived from other 

 plants and animals. 



Animals and non-green plants are therefore 

 dependent, directly or indirectly, upon the 

 substances formed by the green plants for 

 food. This physiological characteristic has 

 led a recent German writer to classify the 

 fungi (mushrooms, toadstools, molds, etc.) 

 among animals. A classification that would 

 work privation to the vegetarian if seriously 

 accepted. 



The action of chlorophyll may best be un- 

 derstood when its physical properties are 



