Zinc, Arsenic , and Boron on the Growth of Plants. 299 
A. Zinc and Arsenic . The facts brought out by the foregoing 
experiments show that there is no sign that zinc sulphate and various 
compounds of arsenic stimulate peas and barley under any circumstances, 
and that the toxic action is very marked, even with quite small quantities 
of the substances. 
This failure to obtain stimulation of peas and barley with very small 
quantities of zinc sulphate might be criticized from the standpoint of 
defective nutrition. The plants are grown in the same solution right 
through the experiment, and it might be argued that stimulation does occur 
in the plants with the least amounts of the sulphate, but that as they 
exhaust their food solution before the end of the experiment growth ceases, 
so that they are ultimately overtaken by the plants with more sulphate, 
which continue their growth longer, as their supply of nutrients is not 
exhausted so early. Analyses of the plants and the food solutions show that 
this supposition does not hold good. At the close of an experiment with 
barley in which the plants had made good normal growth, the used nutrient 
solutions were carefully sampled after the removal of the plants, duplicate 
samples being taken after all the solutions of a given initial concentration 
had been mixed together. The nitrate nitrogen in these samples was then 
determined. Also, the nitrogen present in the dried plants was estimated, 
and the results tabulated and compared. 
Potassium Nitrate present in Original Solution = 1 grm. 
PER LITRE = 0*6 GRM. PER BOTTLE (i PLANT). 
KNO, 
left in sol . 
per litre . 
grm . 
KNO s 
lost from sol . 
per litre , 
grm . 
KNO s 
lost from sol . 
per bottle , 
grm . 
av . wt . KN 0 3 
taken from sol . 
per plant , 
grm . 
kno 3 
not accounted for 
per bottle , 
grm . 
2 
0-885 
0-114 
0-068 
0-042 
0-026 
3 
0-785 
0-214 
0-128 
o-io8 
0-009 
4 
0-699 
0-300 
0-180 
0-142 
0-039 
5 
0-576 
0-423 
0-254 
0-213 
0-040 
6 
0-477 
0-522 
0-313 
— 
— 
7 
0-398 
o-6oi 
0-361 
0-323 
0-037 
8 
0-327 
0-662 
0-397 
0-37 1 
0-025 
9 
0-280 
0-719 
0-43 1 
0-413 
0-018 
10 
0-338 
0-662 
0-397 
o-373 
0-024 
1 1 
0-232 
0-767 
0-460 
0-420 
0-039 
1 
0-237 
0-762 
o*457 
0-428 
0-029 
2 1/10,000 ZnS 0 4 7 1/1,000,000 ZnS 0 4 
3 I /5°, 00 ° „ 8 1/2,500,000 „ 
4 1/100,000 „ 9 1/5,000,000 „ 
5 1/250,000 ,, 10 1/10,000,000 ,, 
6 1/500,000 ,, 11 1/20,000,000 ,, 
1 Control. 
The above table shows that at the close of the experiment over 
20 per cent, of the initial nitrate was left in the solutions by the plants 
