Fig. 9. Photograph showing the action of arsenious acid on barley in the presence of nutrient salts. (March 16th–May 9th, 1911.)
| 1. | Control. | ||
| 2*. | 1/50,000 | arsenious | acid. |
| 2. | 1/100,000 | „ | „ |
| 3. | 1/150,000 | „ | „ |
| 4. | 1/200,000 | „ | „ |
| 5. | 1/250,000 | „ | „ |
| 6. | 1/500,000 | „ | „ |
| 7. | 1/1,000,000 | „ | „ |
| 8. | 1/5,000,000 | „ | „ |
| 9. | 1/10,000,000 | „ | „ |
| 10. | 1/25,000,000 | „ | „ |
| 11. | 1/50,000,000 | „ | „ |
Fig. 10. Curve showing the mean value of the dry weights of ten series of barley plants grown in the presence of arsenious acid and nutrient salts. (March 16th–May 9th, 1911.)
Fig. 11. Curve showing the mean value of the dry weights of ten series of pea plants grown in the presence of arsenious acid and nutrient salts. (June 8th–July 21st, 1910.)
Fig. 12. Curve showing the mean value of the dry weights of ten series of barley plants grown in the presence of arsenic acid and nutrient salts. (Feb. 28th–April 24th, 1911.)
With sodium arsenite the dilutions were carried further, to 1/250,000,000, but this still depressed barley to some extent ([Fig. 13]). With peas the results vary somewhat in the different tests, the depression with 1/2,500,000 and less being usually slight, though occasionally it is much more strongly marked ([Fig. 14]). In a single series with sodium arsenate barley was apparently unaffected by a concentration of 1/1,000,000, but from this point down to 1/250,000,000 a constant depression showed itself, which was paralleled by a similar depression in the sodium arsenite series from 1/25,000,000 to 1/250,000,000, the curves grading downwards instead of up towards the normal. With peas sodium arsenate has little or no action, though it is just possible that the rather irregular curves indicate a very slight depression below the normal throughout.
