214 



Plant Physiology 



the relative effects of light quality. Experiments of this 

 nature are important, especially when the light employed 

 is analyzed as to its energy value. It can be shown 

 that bubbles of oxygen are more rapidly given off, or 

 starch is more rapidly formed, under red-orange screens 

 than under green or blue. Red light is therefore a chief 

 source of the energy used in food-making. 



116. Efficiency of the food-making apparatus. Pains- 

 taking and brilliant investigations have been made upon 

 the energy relations of leaves. The work of green plants 

 is truly remarkable, and it is impressive to consider these 

 organisms as the noiseless machines engaged in the manu- 

 facture of all that organic material upon which life depends 

 the foremost conservators of the energy derived from 



FIG. 57. Ganong's simple light-screen and aerated box for showing the 

 necessity of light in starch-making. 



