1918] Goodspeed-McGee-JIodgson: Effects of Illuminating Gas 449 



may be thought of as bringing about disturbances in normal water 

 relations by increasing the permeability of the leaf septa to favor 

 abnormally high water loss or by a paralysis of the stomatal apparatus 

 with corresponding results. On the other hand, it is at least con- 

 ceivable that a shock effect resulting in a rather complete disturbance 

 of physiological equilibria may be the basic cause of the observed 

 abscission response of plants subjected to poisonous gases. 



V. SUMMAEY 

 The experiments reported upon in detail above were performed to 

 give evidence as to the effect of various concentrations of illuminating 

 gas and of its constituents upon the abscission of flowers of Nicotiana 

 Tahacum var. macrophyUa purpurea, Citrus sinensis varieties Wash- 

 ington navel and Valencia and C. limonia var. Eureka. 



1. In N. Tab. var. macrophyUa purpurea the presence of illumi- 

 nating gas in the atmosphere surrounding flowering laterals caused 

 the first flowers to fall in approximately one-half the normal time. 

 The reaction time was approximately the same in all concentrations of 

 illuminating gas. 



2. Of the constituents of illuminating gas, carbon monoxide, carbon 

 dioxide and ethylene caused premature abscission. 



3. All the experiments with the exception of two were carried on 

 in a moist atmosphere. In these two cases the effect of a dry atmos- 

 phere containing in the first case 10 vol. % illuminating gas and in 

 the second 5 vol. % ethylene was observed. In the first, abscission was 

 so retarded that the first flower fell after approximately the same 

 length of time as the control. In the second, the first flower fell almost 

 as soon in the dry as in the moist atmosphere, and in both cases con- 

 siderably earlier than in the control. 



4. In the case of C. sinensis, variety Washington navel exhibited a 

 marked abscissional response to illuminating gas and did so irrespec- 

 tive of its concentration. In illuminating gas C. sinensis variety 

 Valencia and C. limonia variety Eureka showed little or no increase in 

 the reaction time of the abscission process. 



LITERATURE CITED 

 Balls, W. L. 



1912. The cotton plant in Egypt. London. 



Brown, H. T., and Escombe, F. 



1902. The influence of varying amounts of carbon dioxide in the air on 

 photosynthetic process of leaves and the mode of growth. Proc. 

 Roy. Soc. London, vol. 70, p. 397. 



