284 Brenchley. — On the Action of Certain Compounds of 
a strength of poison which is toxic in water cultures may exercise a stimu- 
lant action in soil, and further, a substance may stimulate in soil cultures 
which only exerts a toxic or indifferent action in water cultures, no matter 
how small the quantity in which it is presented. 
Consequently, in considering this question of toxic and stimulant 
action, it is essential that the experimental methods are given due con- 
sideration. When that is done, it is possible to balance up the various 
results, and finally to obtain a more accurate idea of the true action of 
a substance than when one method only is considered. 
The work in the Rothamsted botanical laboratory is confined to the 
water-culture method, and the action of zinc sulphate, arsenic compounds, 
and boric acid, chiefly on peas and barley, has been tested, to follow up 
the work published in 1910 on the action of copper sulphate and manganese 
sulphate on barley. 1 
In each scale of concentrations represented in the curves, a convenient 
intermediate strength is selected as a unit, and all other concentrations in 
the series are expressed in terms of that unit. Thus, with 1/1,000,000 as 
the unit, the scale of concentrations might run thus : — 
IO* 
1/100,000 
4 * 
1/250,000 
2* 
1/500,000 
I* 
1/1,000,000 
°*5 
1/2,000,000 
0-1 
1/10,000,000 
10 
0 
6 
1/20,000,000 
o* 
Control. 
Zinc Sulphate. 
Zinc is one of the elements whose compounds are well known to be 
toxic to plant life. It is generally assumed that the flora of soils containing 
a considerable amount of zinc is specialized, partly in that only a limited 
number of species occur, and partly in that certain morphological differences 
are to be observed between plants of the same species on the calamine soil 
and on ordinary soil. The toxicity of the element has been fully proved 
by various investigators, and the point now at issue is that of a possible 
improvement of growth by means of zinc compounds applied in very small 
amounts. This point has been tested at Rothamsted, anhydrous zinc 
sulphate being used throughout the experiments. 
Barley . High concentrations of zinc sulphate, 1/10,000 and upwards, 
kill barley plants. With 1/10,000 zinc sulphate, death does not ensue 
1 Brenchley, W. E. : The Influence of Copper Sulphate and Manganese Sulphate upon the 
Growth of Barley.’ Ann. Bot., vol. xxiv, pp. 571-83 (1910). 
