292 Brenchley . — On the Action of Certain Compounds of 
of 1911, the limit of toxicity was found to be 1/2,500,000 sodium arsenite, 
beyond which growth was unaffected, the dry weights of both root and 
shoots showing practically flat curves (Curve 11). On the other hand, with 
plants grown in the early part of 1913 (January to March), strong growth 
was made even with 1/250,000 sodium arsenite, but although with decreasing 
amounts of poison a gradual improvement in growth occurred, the plants 
100 2D 10 4- 2 I '4- -2 •: -04- -02 0 
1= 1:1,000,000 
Curve ii. Showing the mean values of the dry weights of ten series of pea plants (‘Sutton’s 
Harbinger’^ grown in the presence of sodium arsenite and nutrient salts. (Aug. 10-Sept. 18, 1911.) 
1=1'. 10,000,000* 
Curve 12. Showing the mean values of the dry weights of five series of pea plants (‘ Sutton’s 
Harbinger’) grown in the presence of sodium arsenite and nutrient salts. (Jan. 16-March 25, 1913. 
never quite attained the normal development in any concentration down 
to 1/100,000,000 sodium arsenite. This constant depression only affected 
the shoot growth, as the roots were practically normal in development with 
strengths of sodium arsenite below 1/1,000,000. 
Sodium Arsenate. 
Comparatively few experiments have been carried out with this 
arsenic compound, but the indications are that sodium arsenate does not 
act as either a toxic or stimulative agent within wide limits of concentra- 
