8tbtjctuke and GKOWTn. 29 



the crude sap furnished them by the roots. It is only under 

 the influence of light that they decompose the carbonic acid 

 gas from which the large proportion of carbon they require is 

 obtained. It is to light also that they owe their green color. 

 In the dark this coloring matter is not formed, potatoes and 

 other vegetables kept in cellars throwing out white stems and 

 leaves. Some plants, however, require less light than others, 

 and flourish in shady places. When we wish to blanch a plant, 

 as in the case of celery, we exclude the light.* 



* For a further elucidation of the various subjects discussed in the foregoing 

 pages, see Lindley's "Theory of Horticulture," Gray's "Botanical Text- 

 Book," Boussingault's '^ Econmnie Burale," and Darby's "Botany of the 

 Southern States," to all of which, and especially to the first-named, we have 

 been indebted in the preparation of this chapter. 



