Brenchley . — Organic Plant Poisons . /. 451 
Molliard 1 grew radishes under aseptic conditions in glass tubes, offering 
them 1 part in ] ,000 of various nitrogenous compounds added to a mineral 
solution free from nitrogen, with 5 per cent, pure glucose. A control set 
received the same solution but no nitrogen. After six weeks* growth the 
order of usefulness of the compounds, as shown by the mean dry weights, 
was : (1) urate of sodium, (2) aspartic acid, (3) glycine, (4) legumin, 
(5) sodium cyanide, (6) amygdalin, (7) hydrocyanic acid, (8) leucine. As 
a matter of fact the plants with the last three substances did not look much 
better than the controls with no nitrogen. It is difficult to attach much 
importance to these results since the concentration of HCN used — 1/1,000 — ■ 
is most highly toxic to plant life, as the Rothamsted experiments have 
shown, and also the control plants grown under aseptic conditions without 
any source of nitrogen would naturally fail to develop, as there is little or 
no store of nitrogenous reserves in the seed of the radish. 
The toxic action of hydrocyanic acid on plants is as well marked with 
animals. Fungi are as a rule able to resist the action of poisons much 
better than are the higher plants, but prussic acid is a very violent poison 
even for them. 3 
Experiments have been made at Rothamsted to see whether the 
theory of stimulation with weak concentrations holds good with regard to 
hydrocyanic acid. Numerous experiments were carried out with peas and 
barley in water cultures in various strengths of nutrient solutions, and no 
sign of stimulation was found in any case, even with as little poison as 
1 part in 1,000,000,000, below which concentration it is hardly conceivable 
that any effect can be produced. Great care was taken that the prussic 
acid and other substances used were of the highest possible degree of 
purity. The prussic acid was made afresh for each set of experiments, and 
was distilled from pure potassium cyanide and tartaric acid. The distillate 
was taken in distilled water and the concentration of the solutions was 
estimated by Liebigs method with silver nitrate. 
The initial experiments on peas demonstrated the great toxicity of 
hydrocyanic acid. The concentrations ranged from 1/1,000 to 1/10,000,000, 
and the plants were grown in the usual Rothamsted food solution. Within 
two days the plants with 1/1,000 HCN were killed without making any 
development, and not only so, but the green colour had entirely disappeared 
from the plumules. Lower strengths, to 1/10,000, took rather longer to 
kill the plants. A little shoot growth was made in some cases, which 
at first appeared quite healthy, but the roots utterly failed to develop. 
The roots became intensely contracted, thus 
and rapidly lost their turgescence. The attitude of the dying plants was 
most characteristic. The stems shrivelled from the junction with the 
1 Molliard, M. : Bull. Soc. Bot. France, Ivii, 1910, pp. 541-7. 
2 Clark, J. F. : Bot. Gaz., vol. xxviii, 1899, pp. 289-327, 378-404. 
