30 BOTANICAL GAZETTE [jlly 



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, Knight 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 1 0-20-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 10 liters of soil received 

 gas at the rate of about 0.2 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 clays, 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 

 I he gas in the interstices. They were then taken to the greenhouse, 

 placed in shallow boxes, and planted to 41 different species of plants, 



