76 



THE VEGETATIVE FUNCTIONS OF PLANTS 



This means that sunhght is necessary in order to make 

 chlorophyll. But green plants cannot elaborate food in 

 the dark. This means that sunlight is necessary, not 

 alone for the formation of chlorophyll, but for food mak- 

 ing as well. Non-green tissues, even in sunlight, cannot 

 manufacture food; for this process both chlorophyll and 



Fig. 57. — A tree (hornbeam), seen from among the branches (as the 

 squirrel sees it), showing absence of leaves except at or near the tips of the 

 branches. The same tree as in Fig. 56. (Photo by the author.) 



sunlight are necessary. The green cell has often been 

 likened to a factory; the chlorophyll is the machinery, 

 the sunlight is the energy, while the product of the factory 

 is the manufactured food. 



75. Details of the Process. — The manufacture of carbo- 

 hydrates involves three essential steps: 



I. Taking in the raw materials (water and carbon 

 dioxide) . 



