1918] Goodspeedr-McGee-Hodgson: Effects of Illuminating Gas 445 



ones, while open flowers just before anthesis and older flowers are 

 apparently not at all affected. 



Miss Doubt mentions the fact that some species would give no 

 visible response during or immediately following the period of ex- 

 posure to illuminating gas, but that a number of days after the end 

 of the treatment more or less heavy leaf-fall would occur. This is an 

 interesting point, especially when one considers its implications with 

 regard to the factors actually responsible for initiating cell separation. 

 Further, a specific effect of different gases which bring about spon- 

 taneous abscission is suggested in view of the fact that, as contrasted 

 with Miss Doubt's results with illuminating gas, jMoore and Willaman 

 (1917) found that fumigation with hydrocyanic acid causes an increase 

 in permeability of the leaf septa, which is followed by a wilting, etc., 

 from which, however, the treated plants after a time appear to recover 

 completely. It may be noted in this general connection that Hannig- 

 (Lloyd, 1914, p. 68) states that 0.00002 vol. % of illuminating gas 

 caused flower-fall in Mirahilis, etc., while high concentrations em- 

 ployed for fourteen hours did not give the same result directly but 

 did give it indirectly somewhat after the end of the treatment. Lloyd 

 (1916, p. 58) states that cotton bolls "may be shed when one or two 

 days old in relatively high frequences, in response to stimuli applied 

 before anthesis, provided the stimuli applied are severe enough." 



In the case of the experiments with Citrus the controls show a 

 rather wide variation which is sufficient to account for the variation 

 in reaction time shown by the material subjected to gas. It will also 

 be remembered that the percentages of gas stated in table 1 were not 

 so quantitatively correct as in the similar experiments with Nicotiana. 

 Except in the case of variety Washington navel the effect of illumi- 

 nating gas is very slight and for C. limonia one might almost be led 

 to suspect from the results given that gas has no effect in accelerating 

 reaction time. It seems possible that with the exception of variety 

 Washington navel there is a type of rigor effect in the case of the 

 higlier percentages of illuminating gas which inhibits all normal 

 response. Fitting (1911), who showed that laboratory air, carbon 

 dioxide, tobacco smoke, ether, etc., cause premature fall of corolla, 

 also found that rigor induced by heat effects and lack of oxygen tend 

 to inhibit the injurious effects of poisonous gases. Of interest in con- 

 nection with this whole question of the influence of poisonous and 

 anesthetizing gases is the work of Hempel (1911), who has shown that 



2 We have not liad access to the original of TIannig's article. 



