PERIODICAL LITERATURE 787 



The findings may be briefly stated as follows : 



Dust and acid vapors are practically negligible quantities, so far as 

 vegetation is concerned; the average vegetation can stand fifty times 

 the strength of acid vapor that it can resist where the sulphur is admin- 

 istered in the form of SOg. 



Only when the plant is in leaf damage from, sulphur dioxide results. 

 Treating the soil with sulphur or sulphuric acid results in most cases 

 in increased crop production. This is contrary to A. L. Wieler's, the 

 great German smoke expert, findings ! 



Damage to the foliage takes place through the stomata, when they 

 are open, which condition is dependent upon the four factors of light, 

 humidity, temperature, and constant wind direction, producing steady 

 influence of the fumes for several hours. 



The use of small laboratories in automobiles and a rapid method of 

 air analysis, devised by J. R. Marston and A. E. Wells, permitted the 

 determination of constancy or inconstancy of SO2 in the fumes at vary- 

 ing distances from the source. 



The author then rediscovers the old fact, which makes the smoke 

 expert's work so difficult, that "many diseases, pathological conditions 

 and insect injuries, both externally and under the microscope, pre- 

 sent an appearance identical with that of smoke injury." But then 

 he continues with the astounding claim that "in determining the injury 

 of plants by disease we can establish our diagnosis with scientific ex- 

 actness . . . beyond the possibility of doubt or question," namely, 

 by means of cultures and inoculations, and for insect colonies by col- 

 lecting the causative insect. The author overlooks that several troubles 

 may occur together, and it would then be necessary to diagnose primary 

 and secondary causes — the very difficulty that troubles the smoke 

 expert. 



New is, perhaps, at least in method, the use of guide plants, namely, 

 such as are particularly susceptible to fume injury, like barley, which 

 will show most readily whether fume injury is involved. Priority of 

 invention of the method of using guide plants, in this case the sweet 

 pea, may, however, be claimed by Knight and Crocker in their work on 

 the toxicity of smoke. ^ 



A somewhat doubtful claim is made for the benefits which the 

 smelter may confer on agricultural production, or at least from the 

 absence of deleterious efifect, a case of potatoes infected by fungi being 

 cited as an example. 



* Toxicity of Smoke. By Lee I. Knight and Wm. Crocker. Bot. Gazette, May, 

 1913, Vol. LV. 



