Zinc, A rsenic, and Boron on the Growth of Plants. 289 
Peas. Peas are far more sensitive than barley to the higher strengths 
of arsenious acid. With 1/50,000 As 2 0 3 no growth at all is possible, 
even at the very beginning, but the little plants are killed straightway. With 
Curve 6. Showing the mean values of the dry weights of ten series of barley plants (* English 
Archer’) grown in the presence of arsenious acid and nutrient salts. (March 16-May 9, 1911.) 
1/100,000 As 2 0 3 the shoot grows a very little at first, but the roots are killed, 
and within a short time the plant dies. This seems to be the critical point, 
as below this concentration rapid improvement occurs down to a strength of 
0 1 C — — I TT . 
100 20 10 4 2 1-4 -2 -I 0 
1 = 1:1,000,000 
Curve 7. Showing the mean values of the dry weights of ten series of pea plants (‘ Sutton’s 
Harbinger’) grown in the presence of arsenious acid and nutrient salts. (June 8-July 21, 1910.) 
1/2,500,000 As 2 0 3 . From this point onwards the improvement is less well 
marked, and it is just possible that a slight toxic action is slill manifest 
with 1/10,000,000 As 2 0 3 , though this may mark the limit of toxicity and 
the setting in of indifferent action (Curve 7). The concentrations have not 
been pushed further, so that the question of stimulation by smaller doses of 
arsenious acid is not settled. 
