Leaves and Their Structures 



or yellowish instead of green. 

 Light is usually necessary to 

 the development of chlorophyll. 

 The white sprouts on potatoes 

 in a dark cellar, the blanching 

 of celery when the lower part of 

 the leaves is covered, and the 

 whitening of grass under a board, 

 are familiar evidences of this 

 fact. In the inner tissues of 

 plants and in the underground 

 parts, the plastids are usually 



Colorless ; but in many plants FIG. 17. Part of a moss leaf that is 



these parts become green if they com P sed of a sin g* e la y er of cells - 

 are exposed to the light. This is why potatoes that grow at 

 the surface of the soil are likely to be green. 



