40 



Effect of Zinc Compounds 



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 consider- 

 ably, 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 



1-4 - 



i-2 

 1-0 



s 



5 

 4 



TohoJ 



Rool- 



100 



O* 



02 



1 = 1:1,000,000 



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.) 



amount of growth even in the presence of a solution of the anhy- 

 drous salt ZnS0 4 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 J or 1 in | 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 



