1918] Goodspeed-McGee-Hodgson : Effects of Illmninating Gas 447 



In experiments 3, 4, and 5 (table 2) the material was placed in 

 contact with 10 vol. % and 25 vol. % of hydrogen and 10 vol. % of 

 methane, respectively. The time required for the first flower to fall was 

 the same in the treated material as in the controls. The results of the 

 experiments in which hydrogen was employed are included primarily 

 to emphasize the point mentioned in the paragraph above, as there is 

 no reason to suppose that this gas would be effective in initiating 

 abscission. 



The result of experiment 5, in which 10 vol. % of methane was 

 used, shows that this gas has nothing to do with the flower-fall caused 

 by illuminating gas. Knight and Crocker (1913) in studies of toxicity 

 of tobacco smoke found that methane in 0.00001% concentration was 

 not toxic to the etiolated hypocotyl of the sweet pea, carbon dioxide 

 when washed out of the smoke in no wise decreased its toxicity, and 

 that the toxicity of ethylene is so extreme that 1 part in 10,000,000 

 has a marked effect. 



As will be noted in table 2, relatively high concentrations of carbon 

 dioxide, carbon monoxide, and ethylene are effective in bringing about 

 flower-fall in decidedly less than the normal time. The effect of 

 ethylene was to have been anticipated in view of the evidence furnished 

 by a number of investigations which indicate that this gas not only 

 is able to produce marked physiological changes in the plant, but also 

 that to its presence in illuminating gas is attributable the responses 

 which plants give when subjected to small amounts of that substance 

 The results of Knight and Crocker already referred to emphasize this 

 point. Harvey (1913) found for the seedling castor oil bean that the 

 cotyledons fell or the abscission layer was formed after exposing the 

 plants to 1 p.p.m. of ethylene or to 25 p. p.m. of illuminating gas (in 

 this case equal to 1 p.p.m. of ethylene). Doubt {loc. cit.) showed that 

 in various species 5 to 8 p.p.m. of ethylene caused leaf-fall. In at least 

 two cases it is worthy of note that no leaf-fall was reported after 

 treatment with 8 p.p.m. of ethylene, although fall occurred when 

 4000 p.p.m. illuminating gas was used. Undoubtedly fall would have 

 occurred if the concentration of ethylene had more nearly approached 

 that in which it was present in the concentration of illuminating gas 

 which did cause fall. 



Our experiments upon the effectiveness of the constituents of 

 illuminating gas in causing flower-fall are of value mainly in so far as 

 they indicate that carbon monoxide and carbon dioxide are effective. 

 As mentioned above Knight and Crocker {loc. cit.) found that carbon 



