64 Diseases of Greenhouse Crops 



Table lo 



It is thus seen that the greatest transpiration takes 

 place under the yellow light, and the least under 

 the violet. 



Effect of Various Light Rays on the Color of 



Plants 



It is well known that the green color of leaves 

 which is due to chlorophyll can only be produced 

 in the light. Other plant colors such as red, yellow, 

 blue, may be due to the presence of colored pig- 

 ments, or to color in the cell sap itself. 



That light and not temperature is capable of 

 changing the colors in plants has been proven by the 

 investigations of Flammarion. He found that lilac 

 blossoms in a white hothouse became pink, and in 

 red, green and blue hothouses the blossoms became 

 white. If the lilac blossoms already colored are 

 placed under a dark bell jar, they will turn from 

 pale blue to clear red violet. This change of color 



