Zinc , Arsenic , and Boron on the Growth of Plants. 287 
produce flowers and fruit before they die, little shoots an inch high bearing tiny 
dwarfed flowers or equally dwarfed pods. Rapid improvement in growth 
results with decrease in the quantity of the toxic agent. Again some slight 
gm. 
1 = 1:1,000,000 
Curve 4 . Showing the mean values of the dry weights of nine series of pea plants (* Sutton’s 
Harbinger’) grown in the presence of anhydrous zinc sulphate and nutrient salts. (May 18- 
June 28, 1910.) 
difference manifests itself as to the concentration of zinc sulphate which fails 
to exercise a toxic influence upon pea plants. In a series grown early in 
the summer (May-June), very little increase in the dry weights occurred 
gm. 
1-6 
t-4 
1-2 
10 
■8 
•6 
•2 
0 
200 100 20 !0 4 2 I -4. -2 I -05 O 
1 = 1:1,000,000 
Curve 5. Showing the mean values of the dry weights of five series of pea plants (‘ Sutton’s 
Harbinger ’) grown in the presence of anhydrous zinc sulphate and nutrient salts. (Sept. 30- 
Dec. 20, 1912.) 
with concentrations from 1/250,000 downwards (Curve 4). Later in the 
year (Sept.-Dee.) the toxic action was perfectly definite down to 1/500,000 
zinc sulphate (Curve 5). Below these points little action is evident, but 
the dry weights of the plants grown with the small amounts of zinc sulphate 
ToFcd 
5hooF 
RooF 
