Zinc, Arsenic , and Boron on the Growth of Plants . 293 
tion. With both peas and barley it is possible that some slight depression 
occurs with 1/250,000 sodium arsenate, but below this strength, down to 
1/100,000,000, the dry weights of the plants either approach the normal or 
else give a somewhat irregular curve which is probably of little significance 
(Curves 13 and 14). 
40 20 iO 4 2 I -4 -2 I 0 
t = !•• 10,000,000 
Curve 13. Showing the mean values of the dry weights of five series of pea plants (‘Sutton’s 
Harbinger’) grown in the presence of sodium arsenate and nutrient salts. (Jan. 16-March 25, 1913.) 
1«P .'0,000,000 
Curve 14. Showing the mean values of the dry weights of ten series of barley plants (‘ Archer’) 
grown in the presence of sodium arsenate and nutrient salts. (Feb. n-April 18, 1913.) 
Boric Acid. 
The chief experiments to test the action of boric acid on plants were 
carried out with peas and barley, but other tests were also made with 
lupins. The latter plants grew more successfully than is usual for them 
x 
