In a similar investigation in the vicinity of a zinc smelter at Lethmathe, Germany," one especially conclusive examination was made of the foliage of the surrounding vegetation. The investigator, instead of selecting the trees in groups of two from the same location, one injured and the other uninjured, used injured trees from points near the smelter and uninjured trees for comparison at points farther distant from the smelter, but in the same direction. (When this can be done the results are even more conclusive than those obtained by the writer by the method just outlined, but, unfortunately, the rugged nature of the country in the vicinity of the smelter at Redding made such a procedure impracticable.) Of nine groups of trees examined 89 per cent contained more sulphur trioxid both in the leaves themselves and in the ash of the leaves of the injured trees than in the uninjured ones. Three or four years later the same region around the zinc smelter was again examined, and it was found that in nineteen groups of trees the leaves of all of the injured trees contained more sulphur trioxid than those of the uninjured ones. From the work done in the vicinity of Redding, Cal., the following important conclusions are drawn: (1) Sulphur dioxid when present in very minute amounts in the air kills vegetation. (2) The injury is accompanied by an increased sulphur trioxid content of the foliage. (3) The vegetation around the smelter for at least 3 miles north, 9 miles south, 2 miles east, and 5 to 6 miles west, is greatly injured, and less severe injury extends even beyond these limits for a considerable distance (Pls. III and IV). TWO TENNESSEE SMELTERS. The next investigation of injury to vegetation by smelter fumes, conducted by the writer, was made in 1905 and the summer of 1906 in the mountainous country of Tennessee, North Carolina, and Georgia, surrounding two Tennessee smelters, and in the laboratory at Washington. The following counties were examined in the various trips made in the vicinity of the smelters: Polk, Tenn.; Fannin and Gilmer, Ga., and Cherokee, N. C. Again, the only injury studied was that due to the action of sulphur dioxid and trioxid on vegetation. The chemist in this investigation was accompanied by one of the foresters of the Department of Agriculture. Samples of soil and foliage were collected for chemical examination, but the foliage came only from those trees which the forester was reasonably sure had not died from insect pests, forest fires, crowding, or other conditions. a Haselhoff and Lindau, Die Beschädigung der Vegetation durch Rauch. commonly causing the destruction of forests. These samples of foliage were classified by the forester and forwarded to the Bureau of Chemistry for analysis. For purposes of investigation samples of the dead and injured trees surrounding the smelters were examined, as well as of the uninjured trees of the same species beyond the range of apparent injury. The sulphur trioxid content of the foliage and ash of the two sets of samples was then compared. The soils beneath the injured trees were compared with those from beneath the uninjured trees to determine whether any increase in the sulphur trioxid content of the injured trees might be due to an increased amount of sulphur trioxid in the soil. If the sulphur trioxid content of the uninjured trees, situated much farther away from the smelters, is less than that of the injured trees situated near the smelters, and yet the sulphur trioxid content of the soils in which the trees grow is the same, or nearly the same, in both cases, this increase of sulphur trioxid must have been absorbed from the air and must be responsible, wholly or partly, for the death of the trees, since it is known that small amounts of sulphur dioxid and trioxid, when absorbed by the leaves of trees, do kill them. In the absence of insect pests in sufficient numbers to cause great injury, of forest fires, or other ordinary causes for the death of trees, it must be concluded that it was the sulphur dioxid and trioxid alone that caused the damage. Attention is again called to the fact that this method of comparing injured trees with uninjured trees at a greater distance from the smelter is better than the method followed by the writer at Redding, Cal., and should undoubtedly be followed in all cases where such a comparison is possible. The country around the Tennessee smelters easily lent itself to carrying out the investigation in this way, while in the country around Redding, Cal., such a method of working out the problem would have been extremely difficult. In Table II are given the results obtained by examining the foliage of the injured and uninjured trees for sulphur trioxid and ash. In a northerly, easterly, and westerly direction the writer collected and examined samples from beyond the range of apparent significant injury. In a southerly direction a few such samples were collected, but unfortunately they were very wet when gathered and molded during transit. However, since the samples collected beyond the apparent range of injury in an easterly direction grew in a soil containing practically the same amounts of sulphur trioxid as the soils south of the smelters, and also since the examined area to the south is near the area over which the samples were collected east of the smelters, it a U. S. Dept. Agr., Bureau of Chemistry, Bul. 89. is believed that the injured trees to the south can be compared with the uninjured trees beyond the range of significant damage in an easterly direction with perfect satisfaction, and that the results of such a comparison will be just as accurate as though such uninjured samples had been taken beyond the smoke range to the south. It should be borne in mind that two smelters were involved in the above investigation, which were situated so close to one another that it was impossible to say which probably was causing the damage. Hence a point midway between the two was chosen as the most convenient point from which to reckon all of the distances given in Table II. TABLE II.—Sulphur trioxid in foliage, in ash, and in soils around smelters. |