LETHAL GASES 185 



The Jerusalem cherry absorbed much mercury from mercury vapor in the 

 atmosphere but was httle injured by it. Evidently there is a great differ- 

 ence in the resistance of protoplasm of different plants to injury by mercury. 

 Gray and Fuller ^^ found that dry seeds of pea, corn, bean, radish, sun- 

 flower, and cucumber stored in fairly tight chambers with an open beaker 

 of mercury for six months showed no injury. There was a slight delay if 

 the seeds were germinated in the presence of mercury vapor, but the 

 percentage of germination was not affected. Seedlings of these plants were 

 injured by addition of mercury to the substratum or mercury vapor in the 

 air. The injury was somewhat greater under the first condition. In both 

 cases the seedlings were stunted, showed yellowing of leaves, early leaf fall, 

 and failure of leaf development. Kincaid ^^ found mercury vapor in the air 

 toxic to germinating tobacco seeds, especially at higher temperatures and 

 with exposure of large surfaces of the metal. Harrington ^' states that 

 presence of mercury forces dormant Johnson grass seeds to germinate 

 promptly at temperatures that gave no germination in absence of mercury. 

 Giese ^^ has recently emphasized the danger of laboratory workers being 

 poisoned by mercury fumes. A cubic meter of air saturated with mercury 

 at 25° C (77° F) contains 19.5 mg of mercury. A stream of air passing over 

 10 cm^ of mercury at 25° C (77° F) at the rate of 1 liter per minute becomes 

 about 15 per cent saturated and contains 3 mg of mercury per cubic meter. 

 He cites researches to show that prolonged exposure of some individuals to 

 as little as 0.01 mg of mercury per cubic meter and of many individuals 

 to 0.25 mg results in chronic mercury poisoning. Mercury is eliminated 

 from the body slowly and consequently accumulates with continued ex- 

 posure. Giese mentions that Faraday, Pascal and other physicists and 

 chemists suffered from chronic mercury poisoning -svdthout realizing it. 

 Among the symptoms of mercury poisoning are irritability, headaches, and 

 recession of the gums. 



Effect of Sulphur Dioxide on Plants 

 Fifty years ago it was not unusual to see large areas around smelters com- 

 pletely denuded of plants by the large amount of sulphur dioxide released 

 into the air. Extensive studies have been made in both Europe and America 

 on injury to vegetation and even to animals by smelter fumes. These 

 studies have resulted in three great accomplishments. First, very accurate 

 methods have been developed for determining the effect of SO2 on plants. 

 This phase has been especially marked by the designing of accurate instru- 

 ments for automatic recording of the SO2 content of the atmosphere and for 

 fumigating plants A\'ith regulated and automatically recorded SO2 content. 

 Secondly, a great deal of information is now available on the injury to 

 plants by SO 2, the relative sensitiveness of different plants and plant parts 

 to SO2, and the degree of injury necessary to reduce crop yield. Finally, 

 smelters have made use of this scientific knowledge in reducing the injury 

 by SO2 about smelters. They have also removed solid matter from smelter 



