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 MAveER (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. B6xnm (1) 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. 
Mo itscu (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. RicHarps 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, 
