LETHAL GASES 183 



for several days the plants died. In 1867 Boussingault ' repeated some of 

 the experiments, obtaining results comparable to those of the Dutch scien- 

 tists." Since that time several German workers have discussed the poisonous 

 effects of metallic mercury vapors, but no publications have been found 

 which show that the air becomes contaminated where mercuric compounds 

 are applied to the soil." 



The buds of the Briarcliff rose proved especially sensitive to mercury 

 vapor in the air. Very young buds and a region of the stems just below 

 them were killed. In older buds the petals were killed and turned brown, 

 the whole corolla abscissed, and stamens and pistils became black. In old 

 buds the petals which had begun to open lost most of the pink pigment and 

 turned bro^^^l at the edges. Fig. 69 shows the nature of these injuries. 

 It will be noted from Fig. 69B that buds showed the same type and degree 

 of injury whether they grew in pots to which HgCl2 solution was added to 

 the soil or in pots in the same enclosure in untreated soil. The injury in all 

 cases was due to vapor in the air. While the buds were the most sensitive 

 part of the plants, the leaves were also injured with more severe treatments. 

 There was considerable variation in the sensitiveness of different varieties 

 of roses. Of the seven varieties tested (Columbia, Templar, Killarney, 

 Fernet, Madame Butterfly, Mrs. Calvin Coolidge, and Briarcliff), Briar- 

 cliff was the most sensitive and Templar the most resistant. 



Plants of 65 different genera were injured by vapors from metallic mer- 

 cury or from soils treated with HgCl2 solution. Broad bean, butterfly weed, 

 oxalis, and sunflower were especially sensitive. Aloe, croton, and sarcococca 

 were very resistant. The sensitiveness probably depended upon the ma- 

 turity and degree of dormancy of the plants at the time of treatment as 

 well as upon the species. In actively growing peach seedlings a foot or 

 more high, the old leaves were most sensitive and the young leaves most 

 resistant. 



The degree of injury caused by vapors from mercury or soil treated with 

 mercury compounds depended upon several factors. Temperature was 

 very important, as would be expected from the fact that the vapor pressure 

 of mercury rises rapidly with the temperature. Fig. 70 shows that all the 

 leaves are killed on peach seedlings at 75° F (24° C) by vapors from both 

 mercury and soil treated with HgCl2 solution. The injury is less severe at 

 60° F (16° C), slight at 50° F (10° C), and nil at 40° F (4°C). With 

 mercury the injury increased not with the total volume of mercury in the 

 enclosure but with the surface exposed. Covering the mercury with a 

 layer of water 1 cm thick prevented injury. 



The mercury was determined in the leaves of various plants after ex- 

 posure to mercury vapor. No relation existed between the amount of 

 mercury absorbed and the degree of injury produced in the various kinds 

 of plants. Under a given exposure the leaves of the Briarcliff rose absorbed 

 about one-half as much mercury as leaves of Killarney and Coolidge, and 

 yet the leaves of the former were more injured than those of the latter. 



