22 THE SMOKE INVESTIGATION 



General Considerations 



It follows from the above data that injury to vegeta- 

 tion is caused by the smoke and gases given off by indus- 

 trial establishments. In many instances the injury, and 

 sometimes the complete destruction of the vegetation, can 

 be traced directly to smoke and gases accompanying the 

 smoke. In this particular all investigators agree. But 

 this alone does not give much insight as to the specific 

 cause or causes for the injury. It has been determined 

 that smokes vary widely in composition both quantita- 

 tively and qualitatively, and that several gases may be 

 variously associated with each other and with the solids 

 present. This being the case the problem then is to de- 

 termine the extent of the injury of the several substances. 

 On account of the different compositions of smokes in dif- 

 ferent localities the problem is a complex one, one which 

 at the present moment is only partly solved. Many valu- 

 able data have been obtained, but for the most part from 

 the study of the gases occurring with the smoke and only 

 to a slight extent with reference to its solid components. 

 The writer has undertaken to determine the extent of the 

 injury to plants caused by the soot, i. e., by the "fixed 

 carbon" as elsewhere defined and as supplied the writer 

 for this investigation 'by Dr. R. C. Benner. It is the opin- 

 ion of the writer that the final word has not been said in 

 this regard. 



The objection may 'be raised that the effect of a small 

 amount of soot applied over a long period will not be 

 the same as when applied in large amounts during a 

 shorter period, the conditions namely of the experiments. 

 This objection may be well taken, but the writer thinks 

 it not unlikely that there is less weight to be attached to 

 it than at first sight appears. The conditions of 

 the experimentation were, however, unavoidable, and 

 the conclusion must rest on the probability that the larger 



