Effect of Arsenic Compounds 61 



pots. Barley proved even more sensitive than wheat, for even 0-05% 

 arsenious acid affected the growth adversely. After a time the plants 

 with 0'05 — 0-06% recovered and grew strongly, though not so well as 

 the controls, but those with O'lO % practically died off. Eye behaved 

 in the reverse way from wheat. The plants with OlO % were slightly 

 checked at first but later recovered and made growth quite equal to 

 the check plants. Growth was stunted with 0*20 °/ arsenious acid, and 

 the plants were killed with 0-30%, so that rye is far less sensitive 

 than barley. With maize the growth was slightly affected with 

 0"05% AsjOj, and increasingly so with greater quantities. It was 

 also found that the action of 0'8 % AsaOj was strongly adverse to the 

 germination of all plants, and that above this strength germination 

 was altogether prevented. 



The results show very clearly how impossible it is to draw any 

 general conclusions with regard to the action of arsenic compounds 

 on plants, as they emphasise the strong individuality of the species 

 in their reaction. 



3. Do arsenic compounds stimulate higher plants? 



The question of stimulation due to arsenic does not seem to have 

 engaged the attention of investigators to any extent. Water culture 

 experiments at Rothamsted have so far yielded negative results, and 

 no stimulation has yet been obtained with any plajit, with the possible 

 exception of white lupin with sodium arsenite. In a single series 

 a stimulus was suggested, beginning to make itself felt at 1/600,000, 

 rising to an optimum at 1/10,000,000. No stress can be laid on this 

 result, as it is never safe to draw any certain conclusions without 

 several repetitions of the same experiment. With arsenic acid on 

 barley a possible stimulus is sometimes indicated to the eye, the 

 plants being fine and of a particularly healthy dark colour, but this 

 is not corroborated by the dry weights. Additional tests were made 

 with peas and barley, treated with sodium arsenite and arsenate, the 

 dilutions being carried down to 1/260,000,000, but no evidence of 

 stimulus was obtained, so that it hardly seems possible that arsenic can 

 act as a stimulative agent for these two plants when grown in water 

 cultures. It had been thought that the failure to find a stimulation 

 point hitherto might be due to the too great concentration of the 

 toxic substance rather than to the actual inability of the poison to 

 stimulate, but this hypothesis must now be dismissed so far as these 

 plants are concerned. 



