The next year (1883) Storp repeated these experiments made by Krauch and corroborated his results fully. Barley and grasses (timothy and others) grown in solutions of zinc sulphate, both with and without nutrients, soon lost their green colour and became covered with rusty brown flecks, the barley dying within 14 days, and the grasses soon after. With willow, too, the toxic action was again manifested. True and Gies (1903) showed that the addition of calcium salts in appropriate concentrations reduced the toxicity of zinc salts considerably, a result similar to that which they obtained for copper. Recent experiments at Rothamsted have shown that zinc sulphate is very toxic to barley, though the plant is able to make some slight amount of growth even in the presence of a solution of the anhydrous salt ZnSO₄ as strong as 1/5000, rapid improvement occurring as the concentration decreases to 1/2,500,000 or less (Fig. 6). On the whole the higher strengths of zinc sulphate are less poisonous to peas than they are to barley. At a concentration of 1 in ¼ or 1 in ½ million in different experiments the growth was nearly as good as with the control plants, though it consistently lagged a little way behind until a dilution of 1/10,000,000 was reached (Figs. 7 and 8). Incidentally it is very striking to see the desperate efforts that badly poisoned pea plants make to reproduce themselves. Growth of the roots is nearly always checked in advance of that of the shoots, probably on account of the contact of the roots with the poison. In the greater strengths of such poisons as zinc and copper sulphate root growth is checked from the outset, but usually a very little shoot growth is made, and one frequently obtains ridiculous little plants about an inch high bearing unhappy and diminutive flowers, which are occasionally replaced by equally unhappy and miniature fruits. The same thing has also been noticed when unsuccessful attempts have been made to introduce spinach as a test plant for water cultures. [Illustration: Fig. 6. Curve showing the mean value of the dry weights of ten series of barley plants grown in the presence of anhydrous zinc sulphate and nutrient salts. (March 2nd–May 8th, 1911.)] [Illustration: Fig. 7. Photograph showing the action of anhydrous zinc sulphate on pea plants in the presence of nutrient salts. (Sept. 30th–Dec. 20th, 1912.) 1. Control. 2. 1/5,000 zinc sulphate. 3. 1/10,000 „ „ 4. 1/50,000 „ „ 5. 1/100,000 „ „ 6. 1/250,000 „ „ 7. 1/500,000 „ „ 8. 1/1,000,000 „ „ 9. 1/2,500,000 „ „ ] [Illustration: Fig. 8. Curve showing the mean values of the dry weights of nine series of pea plants grown in the presence of anhydrous zinc sulphate and nutrient salts. (May 18th–June 28th, 1910.)] (_c_) _Effect of zinc compounds on plant growth when they are present in soils._