AIR AND LIGHT. 61 



tioii by the plant of carbon in a solid state ; 

 from which, modified by the peculiar vital 

 actions of species, color and secretions are sup- 

 })oscd to result. 



For it is found that the intensity of color and 

 the quantity of secretions are in proportion to 

 the exposure to light and air, as is shown 

 by the deeper color of the upper side of 

 leaves, &c. 



And by the fact, that if plants be grown in 

 air from which light is excluded, neither color 

 nor secretions are formed, as is exemplified in 

 blanched vegetables ; which, if even naturally 

 poisonous, may, from want of exposure to light, 

 become wholesome, as Celery. 



When any color appears in parts developed 

 in the dark it is generally caused by the absorp- 

 tion of such coloring matter as pre-existed in 

 the root or other body from wliich the blanched 

 shoot proceeds, as in some kinds of Rhubarb 

 when forced. 



Or by the deposition of coloring matter form- 

 ed by parts developed in light, as in the subter- 

 ranean roots of Beet, Carrots, &c. 



What is true of color is also true of flavor, 

 which equally depends upon light for its ex- 

 istence ; because flavor is produced by chemi- 

 6 



