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<br />O(j~L~I.?=< <br /> <br />Quoting from the hearings of the Utah Air Conservation committee,.!:/ <br />Harris M. Benedict, an employee of Stanford Research Institute, testi- <br />fied that: <br />"There have been many studies conducted on the effects of sulfur <br /> <br />dioxide on plants. Some of these are field observations and <br /> <br />some are carefully controlled laboratory fumigation studies. <br /> <br />These studies have generally suggested that leaves of sensitive <br /> <br />plants, such as alfalfa and white pine, may develop markings <br /> <br />after eight hours' exposure to .24 to .30 p.p.m. Probably the <br />most inclusive and most thorough of such studies involving field <br />and laboratory results are the investigations of Thomas, O'Gara, <br /> <br />Hill, and coworkers conducted right here in Utah. As a result <br /> <br />of these studies, some 100 species of plants were ranked accord- <br /> <br />ing to their sensitivity to sulfur dioxide. The most sensitive <br /> <br />plant found, alfalfa, was then used in highly refined studies to <br />determine the time of exposure required at various concentrations <br /> <br />to mark the leaves and to reduce or interfere with photosynthe- <br /> <br />sis. The results showed that unless the leaves Were marked, no <br /> <br />permanent effects on the growth of the plant occurred. Although <br />during the exposure itself the rate of photosynthesis might be <br />reduced. However, the photosynthetic rate quickly returned to <br /> <br />normal when the expOsure to sulfur dioxide was stopped, unless <br /> <br />some of the leaf tissue was killed. <br /> <br />i <br /> <br />'The results of these numerous experiments have received world- <br /> <br />wide acceptance and have generally been corroborated by <br /> <br />Dr. Morris Katz (Ind. & Eng. Chern. 41:2450-2465). <br />35 <br />