508 



been thrown out to form a thickly matted mass. The end of the tap 

 root, or what remained of it, was covered with a thick, fleshy knob, not 

 very large, but apparently an extension of the bark of the root. We 

 are not fully satisfied as to whether this condition is due to a deficiency 

 of nutriment in the soil, or to a distinctly poisonous action of the arsen- 

 ical compounds. It would seem, however, that the latter was the case, 

 since the tap-root of the boxes similarly prepared, but containing no 

 arseniates, were perfectly sound. We shall, nevertheless, vary our ex- 

 13eriments with a determination of this point in view. 



Mulder states* that plants may be poisoned by many principles which 

 are poisonous to the animal organism, but holds that they do not attack 

 directly what is called the vital principle, but aft'ect the proximate 

 organic principles of the plants, changing the conditions under which 

 they exist, and thus prevent the transmission of liquids from the roots. 

 In support of this idea he cites the coagulation of the albumen of the 

 plants by the metallic oxides, such as lead, copper, &c. In case of arseu- 

 iates of the alkalies and alkaline earths this woukl scarcely occur, since 

 the acids of arsenic have no such effect upon albumeu, and indeed there 

 is, so far as we know, no fact recorded in which they have been known 

 to form any combination with the other constituents of the plant. In 

 the use of metallic compounds of arsenic, however, this action may pos- 

 siblj^ take place. 



We have also conducted some investigations upon the assimilation 

 of arsenic by plants in case of direct application of Paris green itself, 

 but the results of our experiments seem in this instance also to be of a 

 negative character. The investigation has not been as full as we de- 

 sire, but we shall give the results for what they are worth. Upon a lot 

 of "cow-pea," a leguminous ])lant used as a foddering material in 

 the South, growing in the Department grounds, was freely dusted 

 Paris green as obtained from the shops without any admixture of 

 foreign substances. The material did not, however, seem perfectly un- 

 adulterated. In the first case the amount applied seems to have been 

 too large, as all the plants were killed. Subsequently, however, a mix- 

 ture of Paris green and gypsum, in the proportions usually recommend- 

 ed, was applied, and the small terminal buds and leaves were killed. But 

 in a short time lateral buds appeared, healthy branches developed, and 

 the plants grew thriftily without seeming to be otherwise affected. 

 Examinations of the plant at different stages of growth, by means of 

 Marsh's test, carefully applied, failed in any case to reveal the presence 

 of arsenic. It is, however, possible that, had the plants had an oppor- 

 tunity to mature, arsenic might have been assimilated. In this connec- 

 tion the results of the experiments of Prof. E. W. Davyf are exceed- 

 ingly interesting. Being aware of the fact that nearly all of the 

 sulphuric acid employed in the manufacture of superphosphates 

 in Dublin was made from pyrites, which almost invariably con- 

 tained arsenic, he considered it of some importance to determine whether 

 the arsenic which thus passed into the superphosphates, and must, 

 therefore, be communicated to the soil in the most favorable condition 

 for assimilation by plants, could enter into the vegetable organism. As 

 a preliminary experiment to determine whether arsenic could be taken 

 up by the plant, he watered pease, which had been transplanted into a 

 pot containing rich garden-soil, with a concentrated aqueous solution of 

 arsenious acid. This treatment was repeated every second or third day 

 for more than a week, and then discontinued. At the end ot some 



*Chemistry of Auimal aud Vetretable Physiology. English translatiou, 1840, page 626. 

 + Phil. Mag., vol. xviii, p. 108. 



