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



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

 J. Pierce-' 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 Hower.s 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--' -^ abscission of the 

 leaves of citrus plants when snlj.jccted to an atmosphere containing 

 traces of illuminating ga.s. 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"*' -^ on the 

 eflPects of illuminating ga.s and smoke upon plants has shown rather 

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

 toxicitj' of the ethylene present. It has been shown by E. i\I. Harvey^" 

 that as minute traces as one part per nullion 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 conditi(ms absci.ssion 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. 



Peiree-' 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 i;uai'(l cells of the stoiiiata. resulting in decreased 

 stomatal regulation of traiisj)irati(in. As will be pointed out later, 

 several investigators have concluded that abnormal water loss during 

 a part of the day, resulting in con.siderable fluctuations in the leaf 



2' 1. A Report of an Investigation conilutced for U. S. Department of Justice, 

 191."?, uniiublislied manuscripts in the hands of U.S. Attorney General. 2. Report 

 of Selhy Commission, to l'. S. Bureau of Jfines, 1913. 



2= In Citrus limonia. Slionnard, F., Tlie 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. G3 (1917), pji. 207-24. 



2< The Effect of Illuminating Gas and Ethvlone upon Flowering Carnations, 

 Bot. Gaz., vol. 46 (190S), pp. 2;'59-7G. 



af' Toxicity of Smoke, ibid., vol. ri5 (1913), pp. 337-69. 



=».Sonie Effects of Ethylene on Metabolism of Plants, ibid., vol. 60 (191.')), 

 pp. 193-214. 



27 Expert testimonv incorporated in Records of Federal Court, District of 

 Utah, Salt Lake City.' 



