No. 5292. White oak.-Fumigated 16 times from July 20 to uy 24 with sulphur dioxid 1: 10,000. After 2 fumigations brown spots appeared on the leaves. After 5 fumigations the top leaves were dry and brown. After 16 fumigations all the leaves were dry and brown. The control plant was uninjured.

No. 5294. Scrub pine.-Fumigated twice on July 25 with sulphur dioxid 1:10,000. After 2 fumigations all the leaves were brown, dry, and dead. The control plant was uninjured.

No. 5296. Black oak.-Fumigated 100 times from August 5 to August 30 with sulphur dioxid, 1:50,000. After 29 fumigations the gloss disappeared from the leaves and the young leaves took on a grayish tint. After 100 fumigations all the end buds were killed. The younger leaves were bleached and dotted with brown spots. The old leaves had lost their gloss and were bleached in spots. This tree was observed for three weeks after its removal from the fumigation chamber and no new growth took place. The control plant was uninjured.

No. 5298. Scrub pinc.-Fumigated 34 times from September 3 to September 10 with sulphur dioxid 1:50,000. After 9 fumigations the top needles were somewhat bleached. After 19 fumigations the top needles were entirely killed and the lower needles were killed at the ends. After 34 fumigations all leaves were brown and dry. The control plant was uninjured.

No. 5300. Scrub pine.-Fumigated 96 times from September 12 to October 7 with sulphur dioxid 1:100,000. After 49 fumigations the ends of the young needles were turning brown. After 96 fumigations all the leaves were badly affected, the young needles were brown and dead, the older needles dead at the ends. The control plant was uninjured.

The investigation of the effect of fumigation on plants growing in the open was discontinued at this point on account of a pressure of other work, but will probably be resumed later and even greater dilutions than 1: 100,000 will be used.

SULPHUR-TRIOXID CONTENT OF THE FOLIAGE OF FUMIGATED AND UNFUMIGATED PLANTS.

It was next necessary to determine whether treating plants with sulphur dioxid increased the sulphur-trioxid content of the leaves so that it was present in larger quantities in the leaves of the treated plants than in those of the untreated ones. As a necessary consequence of such an increase, the sulphur-trioxid content of the ash of the fumigated plants would be apt to be higher than that of the ash of the unfumigated plants.

In the work of Von Schroeder and Schmitz-Dumont, previously mentioned, when different parts of the plants were treated with varying strengths of sulphur dioxid, the sulphur-trioxid content of the treated plants was in excess of that of the control plants in every case, and the percentage of sulphur trioxid in the ash of the treated plants was higher than that in the ash of the control plants. The same was found to be true on making analyses of the pines and cowpeas fumigated by the writer." Analyses of fumigated plants grown

a Haywood, U. S. Dept. Agr., Bureau of Chemistry, Bul. 89, p. 14.

in the open, made during 1907 since Bulletin 89 was published, give the following results:

TABLE 1.-Effect of fumigating trees growing in the open with varying strengths of sulphur dioxid, as shown by the sulphur trioxid determined in the foliage.

It will at once be seen from the foregoing table that all of the plants growing in the open which were treated with sulphur dioxid contained more sulphur trioxid in their leaves than the control plants, and that the percentage of sulphur trioxid in the ash of fumigated plants is higher than it is in those not fumigated. These results at once suggest a method for determining whether trees around a smelter were killed by the fumes or died from other causes.

FIELD INVESTIGATIONS OF THE ACTION OF SULPHUR DIOXID FUMES ON VEGETATION.

A CALIFORNIA SMELTER AND CERTAIN FOREIGN SMELTERS.

The next step in the investigation was to determine whether the dead and badly injured trees around the smelting works near Redding, Cal., usually contained more sulphur trioxid than trees of the same species which stood close by in the same soil, but were not killed. Of 25 pairs of trees examined in various directions from the smelter 80 per cent contained more sulphur trioxid in the leaves of the injured trees than in the leaves of the uninjured ones, while 20 per cent showed the reverse. It was further shown that in 80 per cent of the cases the injured trees contained a larger percentage of sulphur trioxid in the ash of the leaves than did the uninjured

trees.a

a U. S. Dept. Agr., Bureau of Chemistry, Bul. 89.