1918] Goodspeecl^McGee-Hodgson: Effects of Illuminating Gas 443 



IV. DISCUSSION 



Kendall (1918, p. 397) investigated the effects of 1.5 vol. % illumi- 

 nating gas upon the abscission of flowers in fifteen species, varieties 

 and hybrids of Nicotiwiia and in thirteen other genera and species of 

 the Solanaceae. Flowering laterals were placed under the influence 

 of the gas and air mixtures for fifteen hours, at the end of which time 

 the amount and extent of abscission was noted. So far as Nicotiana 

 is concerned he found that in four forms (cf. p. 398, table 6) neither 

 buds, young flowers, flowers at anthesis, nor seed capsules were 

 abscissed. In one case young buds only fell. In four cases all buds 

 up to anthesis fell, but no older flowers nor seed capsules. In one 

 form all flowers up to four or five days past anthesis were abscissed, 

 and in three cases all buds and flowers fell. Finally, in one case it is 

 recorded that buds, flowers and fruits w^ere abscissed. Kendall also 

 noted that when 3 vol. % of illuminating gas was used, or when the 

 material was subjected to the 1.5 vol. % of gas for more than fifteen 

 hours, some of the species previously found to be unaffected abscissed 

 their flowers. His results in general indicated that there might be a 

 more or less definite relation between the concentration of poisonous 

 gases in the atmosphere surrounding the plant and the reaction time 

 in spontaneous abscission. 



With these results of Kendall's in mind, interest centered in sub- 

 jecting the same material which he used to varying concentrations of 

 illuminating gas and its constituents. The similar experiments upon 

 induced flower-fall in Citrus varieties seemed of interest from a number 

 of points of view. It has been frequently observed that in fumigating 

 citrus trees with hydrocyanic acid in California there is a heavy leaf- 

 fall, especially when certain weather conditions prevail. Apparently 

 no observations have been made upon the effect of poisonous gases in 

 causing flower-fall in this genus. The results here also serve as a 

 check upon the data gathered from the similar experiments with 

 Nicotiana. 



From the results given in table 1, it is clear that the reaction time 

 in spontaneous abscission is not appreciably hastened by increasing 

 the percentage of illuminating gas surrounding the material under 

 investigation. This fact is emphasized particularly in the case of 

 Nicotiana, where the variations in reaction time both in the controls 

 and in tlic material subjected to the gas are relatively slight. Miss 

 Doubt (1917) has recently made a detailed study of tlie responses 



