loo Relation of Cement Dust to Citrus Vegetation 



TABLE 5 



Data pertaining to further determinations of carbohydrates in fresh new leaves, 

 and cleaned and dusty halves of older leaves, front the same tree. 



(See also Table 4) 



As might be expected, the new leaves showed a slightly greater 

 activity; but this was not enough to imply an injury to the older 

 leaves. 



SUMMARY OF GENERAL CONCLUSIONS. The COating of dust Ott 



orange leaves, adjacent to cement plants, corresponds very closely 

 in composition to the " raw mixture " f rom which cement is made. 



The amount of dust on such leaves is often as much as 0.0034 

 gm. per sq. cm. 



This amount of dust may shut out as much as 80 percent of light 

 from the upper surface of the leaf. 



The exclusion of light from the upper surface of the leaf, by 

 such dust, does not interfere with carbohydrate synthesis. 



The metabolic activity of new leaves was only very slightly 

 greater than that of old leaves. 



Leaves analyzed in May contained nearly one-third more total 

 carbohydrate than those analyzed in November and December. 



