452 Brenchley . — Organic Plant Poisons . /. 
cotyledons upwards, so that the shoots fell over, giving the plants the 
appearance of literally ‘ lying down to die \ This is quite unlike the usual 
phenomenon when pea plants are killed by poison or otherwise, since as 
a rule a fairly upright position is maintained to the very end. With con- 
centrations down to 1/100,000 the plants remained apparently unaffected 
for a day or two, but eventually all were killed and completely withered 
within two or three weeks. In some cases the contraction of the roots was 
so intense that they were completely withdrawn from the solutions. In no 
single instance were any laterals formed, and, as is usual, the roots were 
always seriously affected earlier than the shoots. 
Down to this limit of concentration no ultimate growth had been 
possible under the conditions of experiment. With 1/400,000 HCN, how- 
ever, a change occurred. At the beginning the roots showed contraction 
towards the tips, but there was some attempt to put out laterals, which were 
very short and were chiefly developed above the surface of the water. For 
some long time this condition of affairs continued ; the laterals continued 
to form, but refused to enter the solutions for about four weeks. At last 
they proceeded to elongate, and though the roots remained bunchy in 
appearance and medium in length for some time longer, yet they finally 
became more normal in appearance, though the plants remained rather 
small to the end. 
As the concentrations decreased still farther the symptoms of poisoning 
gradually disappeared and the plants approached the controls more nearly. 
It is probable that some slight toxic action continued to manifest itself even 
with 1 part HCN in 4,000,000 or 10,000,000 solution. It. must be borne in 
mind that the exact concentration at which certain phenomena occur cannot 
be fixed definitely for all experiments. These plants were growing from 
Oct. 3 to Feb. 4, during the slow-growing period of the winter months. 
It is more than probable that the time of year, a.mount of available light and 
heat, and many other factors interact in determining the exact action 
of a particular concentration in any experiment, but still, within a certain 
range, the sequence of phenomena remains constant. 
In the experiments with barley, Feb. 1 6 to April 18, the concentrations 
of HCN ranged from i/j 00,000 to 1/1,000,000,000, and both strong and 
weak food solutions 1 were tested. In both cases with the strongest solu- 
Strong 
Weak 
nutrients. 
yiutrients. 
grm. 
grm. 
Potassium nitrate .... 
. . i-o 
0-2 
Sodium nitrate .... 
— T 
0.5 
Magnesium sulphate 
o -5 
O' I 
Calcium sulphate .... 
0*5 
0. 1 
Potassium di-hydrogen phosphate . 
O' I 
Sodium chloride .... 
0-5 
O' [ 
Ferric chloride .... 
. . 0-04 
0*04 
Distilled water, to make up . 
. . 1 litre 
1 litre 
