8 THE SMOKE INVESTIGATION 



ifornia caused a decrease in crop production by covering 

 the leaves with an incrustation of dust and thereby inter- 

 fering with the energy relations. Parish (15) estimated 

 that the lemon crop in the vicinity of the Stower Moun- 

 tains was cut down one-fourth on account of the presence 

 of a large cement factory. He points out that while the 

 stomata are not clogged with dust, nevertheless this inter- 

 feres with photosynthesis. Ruston (17) found in the 

 vicinity of Leeds, England, that a black adhesive film 

 covers the leaves of many tress, particularly evergreens, 

 and thereby interferes with photosynthesis. He further 

 reports that eighty per cent, of the Fir leaves had their 

 stomata clogged. Crowther and Ruston (5) found that 

 impurities in the air were present in large quantities in 

 and a'bout industrial centers. They found that the sus- 

 pended matter brought down by rains has an injurious 

 effect upon vegetation, by direct action on the leaves ; and 

 indirectly by reducing the activity not only of the neces- 

 sary ammoniacal fermentation of the soil humus, but even 

 more of the 'beneficial nitrifying and nitrogen-fixing organ- 

 isms in the soil. Gatin (6, 7) found that various tar prod- 

 ucts used in road pavements were injurious to vegetation 

 and that the effects might be produced by the action of 

 the various gases ; and 'by the action of the dust. He found 

 that the fumes of tar brought about the alteration in the 

 size and num'ber of layers in the cortex and other regions 

 of the stem, and the transformation of dou'bly compound 

 leaves into singly compound leaves. He also reported the 

 disappearance of starch and the formation of cork in leaf 

 organs and stems. Molisch (13, 14) found that tobacco 

 smoke had a marked injurious effect upon micro-organisms. 

 Cohen and Ruston (3) brought together the records of 

 their observations which had been carried on at intervals 

 during the past twenty years. They gave data concern- 

 ing the composition of soot collected from the bottom and 

 top of chimneys of dwellings as well as from the boilers 

 of a number of factories, finding, of course, that the soot 

 varies considerably, depending upon the conditions under 

 which the coal was burned. They also obtained data rela- 



