30 BOTANICAL GAZETTE [JULY 
mixture and the illuminating gas contained approximately the same 
amount of ethylene. In the following experiments, where the 
term ‘‘ethylene in corresponding concentrations to the illuminating 
gas’’ is used, it refers to the ethylene content of the latter gas. For 
example, the ethylene concentration corresponding to an illuminat- 
ing gas concentration of one part gas to four parts of air (‘‘1:4’’) 
would be one part ethylene to 100 of air (‘‘1:100”’). Such parallel 
experiments were considered important owing to the fact that 
ethylene has been found to be by far the most toxic constituent 
of illuminating gas for the aerial organs of several plants (see 
CROCKER and KNIGHT 2, Knicut and CRocKER 7, and Harvey 6). 
The experiments were primarily arranged so as to yield evidence 
with regard to the two phases of the second problem above. The 
methods will be described separately and in the order named. 
Investigation of the second problem should yield data with regard 
to the first. 
A. THE TOXICITY OF THE CONSTITUENT OF ILLUMINATING GAS 
ABSORBED BY THE SOIL 
Good potting soil in 10o-20-liter cans was treated with illuminat- 
ing gas by allowing the gas to flow through at a definite rate, at 
room temperature, for varying lengths of time. The rate of flow 
was approximately 2 liters per hour. The time periods were from 
30 hours to 20 days, hence the lots of soil received 40-1000 liters 
of gas. The moisture content of the soil was kept as near the ‘‘op- 
timum”’ as possible. In one experiment 1o liters of soil received 
gas at the rate of about o.2 liter per hour for 68 days. In another 
experiment 8 liters of soil received gas at the rate of 2 liters per hour 
for 53 days, and was kept at a temperature of 1-5° C. throughout 
the period. The purpose of this soil treatment was to allow the soil 
particles to absorb as much of the gas constituents as possible. In 
the case of treatment at low temperature, it was the intention to 
allow still better opportunity for condensation of substances on the 
soil particles. After stopping the flow of gas, the soils were removed 
from the cans and thoroughly stirred in pure air to free them from 
the gas in the interstices. They were then taken to the greenhouse, 
placed in shallow boxes, and planted to 41 different species of plants, 
