96 



Relation of Cement Dust to Citrus Vegetation 



CoMPOSiTiON OF DUST FROM ORANGE LEAVES, In Order that 

 there might be no doubt that the coating found on the leaves was 

 actually composed of dust from cement-stacks, samples were col- 

 lected and analyzed. In Table i are given the percentages of 

 silica, ferric and aluminum oxides, and calcium oxide, for a sample 

 of the "raw mixture" (the material fed into the kiln at the base 

 of the Stack), and of three samples of dust-coatings from leaves. 

 These three samples were taken from trees approximately a half 

 mile, a mile, and a mile and a half, respectively, from the plant of the 

 Riverside Portland Cement Co. 



TABLE I 



Data pertaining to the composition of dust from Stack and from orange leaves 



The figures in Table i agree closely enough to establish the fact 

 that the dust on the leaves consisted chiefly of material from the 

 kiln-stacks. 



Amount of dust on leaves. The amount of dust on the leaves 

 varies greatly, of course. As has already been pointed out, there 

 is little or no rain here from April to November, a condition that 

 allows the dust to accumulate to a much greater extent than would 

 be the case in a humid region. To determine the maximum amount 

 deposited, a sample of 51 leaves was picked from trees quite close 

 to the cement-plant in November, 1910. The total green-weight of 

 the leaves was 29.96 gm. when picked; the total area was 1178.87 

 cm. The amount of dust was 4.04 gm. or 0.079 gi^i- P^r ^^3.i. 



Av. wgt. of leaf 



590 mgm. 



Av. area 



23.11 sq. cm. 



Av. amount of dust 



79.0 mgm. 



Av. amount of dust per 

 sq. cm. 



3.4 mgm. 



Percent of light excluded from the leaf by the dust. 

 Since the primary object of this investigation was to determine the 

 effect of the dust on photosynthesis. the amount of light excluded 



