EFFECT OF SULFUR DIOXIDE
ON WHEAT DEVELOPMENT Action at Low Concentrations ROBERT E. SWAIN
AND
ARTHUR B. JOHNSON
Stanford University, California
,
QT
HE production
Of dioxide and its subsequent discharge into the atmosphere Of metallurgical and Other inas a dustrial operations has given rise to one of the most baffling problems which these industries have had to face. This gas, a s one of the common constituents of the smoke from furnace operations, is injurious to plant life under conditions favorable to its action and may give rise to typical foliar injury on the more sensitive plants when present in concentrations around one part of sulfur dioxide to one million parts of air, and a t higher concentrations may lead to the complete defoliation and death of the plant. Especially in agricultural or forested regions, where large-scale smelting operations, based upon sulfur-bearing ores, are carried on, this waste Product has often been the cause of bitter and expensive ContrOversY and litigation. Throughout most of the history of the long period of conflict between metallurgical and agrarian interests, particularly in Germany and the United States, the claim has often been made that sulfur dioyide, if present in the air in amounts even below those Concentrations necessary to produce the typical visible signs of its actions on the leaves, exerts an injurious effect upon plant life. This claim of “invisible injury,” which has been strongly supported especially by some of the German investigators (S), is one of dowinant interest and importance. For if it is true that concentrations of sulfur dioxide in the air, well below the known threshold of visible injury for a given plant as indicated by the characteristic foliar markings, are definitely injurious to plant growth or reproduction, the question broadens in its significance. The demonstrated presence of sulfur dioxide in the air, which to some degree is often practically unavoidable in many industrial regions, would then become a valid cause for alarm and legal action. This claim, although often made, has not been supported by convincing experimental evidence. Much of the support for this theory has come from field observations made in the regions adjacent to plants where smelting and other industrial operations were in progress. The uncertainty of this evidence must be conceded. It is clouded by too many variables. For example, in every industrial region where sulfur dioxide is found in notable amounts in the atmosphere, other substances such as soot, tarry materials, and other finely divided products volatile a t high temperatures or mechanically swept as solids from furnace operations, may confuse the picture. These may lead to an abnormal clogging of the stomata of the plant
leaf, or to a reduction in the local light intensity by persistent atmospheric haze, or in some instances may exert a direct effect upon the fertility of the soil. Yo study of plant life in such an area could overlook the possible effect of such factors. If the vegetation did not flourish in it as in regions more remote, and the visible characteristic foliar markings of sulfur dioxide were absent, it would be an unwarranted assumption to ascribe the condition to sulfur dioxide alone. Sulfur dioxide in appreciable amounts is nearly always found in smoky atmospheres and has had to take a large share of the blame for an unflourishing condition of the vegetation in of such regions, but clean-cut proof of its action as an agent injury has often been lacking. In addition to open field observations, many investigations of its action have been made on plants in pots or flats. These have been exposed to low concentrations of sulfur dioxide by such as carbon burning a known weight of a sulfur disulfide, or by the direct introduction of a measured volume of sulfur dioxide into a closed or cabinet in which they were placed. ln later work duplicate setsof small field plots, j or g feet square, were covered with movable cabinets of celluloid and a currentof air, carryingknown concentrations of sulfur dioxide for the test plots and air alone for the controls, was sentthrough tl.lem for the desired period of daily fumigation, The extensiveand painstaking work done thus far in this direction by O J G (8) ~ and ~ ~ later by ill (6) and their eo-workers deserves particular mention. Their investigatiolq however, have been directed more to the causes and conditions and consequences of visible injury than to the question of (
