28 BOTANICAL GAZETTE [July 



roots as well as in the soil; in fact, these odors form the chief diag- 

 nostic characters. Stone (15) claims much for them, and it is 

 probably true that in many cases they furnish some evidence. 

 However, many instances are known where illuminating gas 

 odors have not given sufficient evidence for fixing responsibility. 

 A rational system of diagnosis of injuries in city trees would be 

 of value and would be welcomed by all parties concerned. No 

 such system, from the gas injury standpoint, is possible, owing 

 to the lack of definite knowledge concerning the effects of the 

 constituents of illuminating gas under various controlled conditions. 

 The experimental work previously done on gas injuries to root 

 systems will be briefly summarized. Kny (8) passed known 

 amounts of illuminating gas through the soil at the roots of a maple 

 and two linden trees. Among the symptoms of injuries recorded 

 were the bleaching and final fall of leaves and the appearance of a 

 blue coloration in the xylem of the roots. Finally the trees died. 

 Spath and Mayer (14) passed small amounts of gas into soil in 

 which grew a number of species of trees and shrubs. General 

 death resulted, but otherwise the only symptom recorded was the 

 yellowing of the leaves. Bohm (i) grew willow slips in water into 

 which he had passed a stream of illuminating gas. The short 

 roots produced soon died, but the slips themselves lived for three 

 months. Potted plants of Fuchsia and Salvia died after gas had 

 flowed to their roots for four months. Again, he found that when 

 gas had been passed through a soil for a long period of time, this 

 soil became very toxic to seedlings germinated in it. Also a 

 Dracaena transplanted to this soil became dry and died in ten days. 

 Molisch (10) found that roots of corn increased in diameter and 

 were bent in certain concentrations of illuminating gas. Shon- 

 nard (13) noted exudation of sap from the trunk and branches 

 of a lemon tree treated with gas in the soil. Richards and Mac- 

 dougal (11) found that carbon monoxide and illuminating gas 

 retarded the rate of elongation of roots of Vicia Faba, sunflower, 

 wheat, rice, etc. Swelling also appeared in the leaf sheaths of 

 wheat, being somewhat more pronounced in illuminating gas than 

 in carbon monoxide. Such increases in thickness were largely due 

 to the enlargement of the cortical cells. In some cases, however, 



