58 Effect of Arsenic Compounds 



Gorup-Besanez (1863) mixed 30 grams arsenious acid with 30'7 litres^ 

 soil, growing two plants on this quantity of earth. Most of his experi- 

 mental plants (Polygonum Fagopyrum, Pisurn sativum, and Secale cereale) 

 developed normally, but Panioum italicum died soon after the plants 

 appeared above the surface, the leaves being very badly coloured. 

 Analyses by Marsh's test showed no trace of arsenic in 20 grams dry 

 matter from Secale cereale, but in 148 grams Polygonum Fagopyrum 

 the presence of arsenic was evident, though the mirror formed was 

 weak. With such a large proportion of arsenious acid in the soil it 

 seems hardly conceivable that the plants were not injured to some 

 extent, and also it is probable that with more careful analyses arsenic 

 would have been detected in those instances in which its presence was 

 denied. Yet it must be remembered that Davy (1869) had treated 

 pea plants in pots with a saturated solution of arsenious acid for a 

 short time and had stated that the plants were uninjured. Thus both 

 Gorup-Besanez and Davy concur in the opinion that Pisum sativum 

 is indifferent to relatively large quantities of arsenious acid when 

 presented in the soil, whereas the Rothamsted experiments show that 

 in water cultures the plant is extremely sensitive even to minute 

 traces of the substance. It is possible that the arsenic in the solu- 

 tion added to the soil enters into combination with other substances, 

 forming insoluble compounds, thus being removed from the sphere 

 of action and rendered unable to affect plant life. If this be so, the 

 apparent immunity of certain plants to arsenious acid is explained. 

 F. C. Phillips (1882), in his experiments on various flowering plants, 

 such as geraniums, coleas and pansies, found that compounds of arsenic 

 in the soil exercised a distinct poisoning influence, tending, when 

 present in large amount, to check the formation of roots, so that the 

 vitality of the plant was so far reduced as to interfere with nutrition 

 and growth, or even to kill it outright. He also stated that traces of 

 arsenic were found in all the plants grown upon the poisoned soil. 



In this connection it is interesting to note that a certain proportion 

 of arsenic is frequently present in the superphosphate used as manure. 

 In view of the known toxicity of arsenical compounds to plant life the 

 question arose as to whether superphosphate manuring would exercise 

 a detrimental influence on account of its arsenic content. Experi- 

 ments carried out by Stoklasa (1898), however, indicate that there is 

 not sufficient arsenic in maximum doses of superphosphate to exercise 

 a toxic action in the field. 



' 30 grama areenious aoid to 30 •? "oubik Decimeter" soil = about •! °l„. 



