1919] Coit-Hodgson: Abnormal Shedding of Washington Navel Orange 295 



a combustion product in the reduction of sulfur-containing ores. G. 

 J. Pierce 21 has shown that when SO, is present in as small quantities 

 as three to five parts per million abscission of the leaves of certain 

 forest plants occurs. Several investigators have reported abscission 

 of flowers and leaves of various plants when subjected to minute traces 

 of illuminating gas, ether, chloroform, ethylene, and other poisonous 

 gases. Further, two investigators have reported 22 * 23 abscission of the 

 leaves of citrus plants when subjected to an atmosphere containing 

 traces of illuminating gas. We have obtained similar results with 

 potted plants. Within four days after subjection to illuminating gas 

 all the leaves were shed. 



The exhaustive work of L. I. Knight and W. Crocker 24, 25 on the 

 effects of illuminating gas and smoke upon plants has shown rather 

 conclusively that the response is largely if not entirely due to the 

 toxicity of the ethylene present. It has been shown by E. M. Harvey 28 

 that as minute traces as one part per million are sufficient to cause 

 marked reactions on the part of the plant. 



Preliminary experiments carried out in our laboratories with 

 excised citrus shoots subjected to various gases, including illuminating 

 gas, have indicated that under such conditions abscission is not appre- 

 ciably accelerated by any of the gases. The time at which shedding of 

 the leaves took place was approximately the same in ordinary room 

 atmosphere as in varying concentrations of illuminating gas. 



Peirce 27 has shown that one of the effects of smelter fumes is to 

 cause excessive transpiration from certain plant parts prior to their 

 abscission. This is accounted for by the decomposition of the 

 chlorophyll in the guard cells of the stomata, resulting in decreased 

 stomatal regulation of transpiration. As will be pointed out later, 

 several investigators have concluded that abnormal water loss during 

 a part of the day, resulting in considerable fluctuations in the leaf 



21 1. A Report of an Investigation condutced for U. S. Department of Justice, 

 1913, unpublished manuscripts in the hands of U. S. Attorney General. 2. Report 

 of Selby Commission, to U. S. Bureau of Mines, 1913. 



22 In Citrus limonia. Shonnard, F., The Effect of Illuminating Gas on Trees, 

 Yonkers, N. Y., Dept. Pub. Works (1903), p. 48. 



23 In Citrus decumana. Doubt, Sarah S., The Response of Plants to Illuminat- 

 ing Gas, Bot. Gaz., vol. 63 (1917), pp. 207-24. 



2 * The Effect of Illuminating Gas and Ethylene upon Flowering Carnations, 

 Bot. Gaz., vol. 46 (1908), pp. 259-76. 



2 5 Toxicity of Smoke, ibid., vol. 55 (1913), pp. 337-69. 



26 Some Effects of Ethylene on Metabolism of Plants, ibid., vol. 60 (1915), 

 pp. 193-214. 



-i Expert testimony incorporated in Records of Federal Court, District of 

 Utah, Salt Lake City. 



