188 GROWTH OF PLANTS 



of plants. The findings have been made generally available to industry, to 

 the public, and to science. Much credit is due the director, Dr. George R. 

 Hill, for the public-spirited and thoroughgoing scientific way in which the 

 researches have been managed, and to Dr. Moyer D. Thomas for his 

 unique ability in designing apparatus and planning and carrying through 

 experiments for solving difficult problems in plant physiology. 



Research by National Research Council of Canada. The best case history 

 we have of fumes from a larger smelter is that of the Trail Smelter in the 

 upper Columbia Valley, British Columbia, about ten miles north of the 

 international boundary. The researches were conducted by eight specialists 

 of the National Research Council of Canada, and are published m a 447- 

 page volume. 21 The book reports the observations and experiments of this 

 group and reviews the earlier literature on the subject. Part I (206 pages, 

 including several inserted two- or three-page plates) covers the field studies. 

 The introduction gives the history of Trail Smelter, the amount of SO2 

 emitted by it yearly from 1900 to 1935, and also in 1937, SO2 abatement 

 methods adopted, and history of the international tribunal dealing \\ith 

 claims of United States farmers for SO2 injury. Other subjects covered by 

 the first part are: SO 2 content of the atmosphere m industrial regions, 

 including the Trail region; symptoms of SO 2 injuries on plants; and the 

 effect of the SO 2 content of the air on the sulphur content of trees and 

 shrubs, on the acidity, base-exchange capacity, and sulphur content of 

 soils, and on the gro^^'th in diameter of trees. Part II describes numerous 

 fumigation experiments on forest and crop plants, including a study of the 

 effect of environmental factors on susceptibility of barley and alfalfa to 

 SO 2 injury. It discusses the effect of SO 2 fumigation on stomatal behavior; 

 on crop yield when the fumigation is in tissue-killing and sub-killing 

 dosages; and on photosynthesis, respiration, and chemical composition of 

 plants. The Thomas recorders were used extensively in these investigations 

 and modifications of the Hill and Thomas fumigatmg apparatus were used 

 throughout the fumigating experiments. 



This work has added many accurate data and sound generalizations to 

 our knowledge of the effect of SO2 on vegetation. Space will permit the 

 mention of only two of the generalizations. The "invisible injury" findings 

 of Hill and Thomas were confirmed, that is, there was no reduction in crop 

 yield unless the fumigations were sufficient to kill leaf tissue. Ethylene is 

 an ideal gas for producing "invisible injury " because it is a growth inhibitor 

 and does not kill tissue, as pointed out in the last chapter. It will, however, 

 reduce growth rate only so long as it is in the air surrounding the plant. 

 The SO2 in the leaves was oxidized to sulphates, apparently completely in 

 light fumigations and partially in heavier fumigations. It is the unoxidized 

 SO2 or sulphites that kill leaf tissue. Leaves of evergreens growing m the 

 SO2 belt some distance from Trail showed three to four times the normal 

 content of sulphur without any effect on the color of the leaves and without 

 any retardation in growth. It is likely that the oxidation of SO2 to sulphates 

 accounts for the lack of "invisible injury." 



