STUDIES ON THE RELATION OF CEMENT DUST TO 



CITRUS VEGETATION 



I. The effect on photosynthesis 



H. D. YOUNG* 



(Pathological Lahoratory, University of California, Whittier) 



(Received for publication, June 20, 1915). 



Introduction. The effect of the dust arising from the rotary 

 kilns, in the manufacture of Portland cement, on the surrounding 

 Vegetation has been the basis of considerable investigation. In 

 Southern Cahfornia it has become a problem of importance because 

 of several characteristic factors. There are here some rather large 

 cement-plants in the heart of a prosperous citrus district. As this 

 is naturally a semi-arid cHmate and dependent on irrigation, there 

 are no frequent rains to wash the dust from the leaves and, since 

 the trees are not deciduous, the leaves with their dust-coating are 

 not dropped annually. Because of the great value of the interests 

 involved, the effect of the dust on the trees has recently been the 

 subject of a great deal of litigation. 



In this connection the possible interference of the dust with 

 photosynthesis, by excluding the light, was considered. Peirce^ 

 found that orange leaves showed, in halves which had been freed 

 from dust in the morning, " four or five times as many grains of 

 starch as those in the covered and shaded half." As this would 

 mean a very serious interference with photosynthesis, an investiga- 

 tion was undertaken to see whether or not it held true generally on 

 dusty leaves. 



* The author wishes to express his indebtedness to the Riverside Portland 

 Cement Company, Riverside, California, which defrayed the expenses of this in- 

 vestigation, and to Professor R. E. Smith, University of California, for his many 

 helpful suggestions. 



iPeirce: "An effect of cement dust on orange leaves," Plant World, 1910, 

 13, P. 283. 



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