Science of Gardening. 683 



appear, at first sight, inconsistent with those deduced by M. De Saussure, in 

 his elaborate work on vegetation before referred to ; in which he has shown 

 that some poisonous substances, such, for example, as salts of copper, are 

 freely absorbed by the roots of vegetables, and retained, in considerable 

 quantities in their tissue. But it will be recollected that this philosopher 

 himself accounts for the circumstance by the disorganisation which such 

 bodies, by their presence, occasion in the fibres of the roots. I have myself 

 found that, when a pelargonium had a portion of its roots immei*sed in a 

 solution of bichromate of potass, a trace of this salt was conveyed into a 

 second glass containing distilled water, which had no connexion with the 

 former except through the medium of a parcel of the roots which dipped into 

 it. Nor was this owing to capillary attraction; for the same effect did not 

 take place in another experiment, in which the roots were detached from the 

 body of the plant, and therefore acted as dead matter; and, moreover, the 

 salt was detected by appropriate tests applied to the stems and leaves. In 

 this instance, then, the substance was seen to circulate through the whole 

 texture of the vegetable, and ultimately to be excreted by its roots : and a 

 similar result was obtained in the case of another plant, in which a solution 

 of protosulphate of iron had been dissolved in the water in contact with its 

 extremities. That is to sa}', the salt was detected, by ferro-cyanate of potass, 

 in many parts of the stem and branches ; but it did not reach above a certain 

 point, nor was it excreted by the roots ; this difference arising from the 

 absorption of oxygen by the salt, which, being thereby converted into a 

 persulphate, became insoluble in the juices of the plant, and consequently 

 clogged up the canals by which the sap is conveyed. 



" But, in all these instances, the poisonous quality of the substance was 

 evinced by the more or less rapid decay of the plant that had imbibed it; 

 whereas, where nitrate of strontian was employed, the functions of life ap- 

 peared to go on, for a considerable time, without material obstruction. 



" Upon the whole, then, I see nothing, so fas as experiments have yet gone, 

 to invalidate the conclusion, to which the preceding facts appear to lead, that 

 the roots of plants do, to a certain extent at least, possess a power of se- 

 lection ; and that the earthy constituents, which form the basis of their solid 

 parts, are determined, as to quality, by some primary law of nature, although 

 their amount may depend upon the more or less abundant supply of the 

 principles presented to them from without." (p. 176.) 



The Effects of Arsenic on Vegetation. — Dr. Daubeny communicated to the 

 British Association at Bristol, " the partial results which he had obtained from 

 a series of experiments he was carrying on at Oxford, respecting the effects 

 which arsenic produces on vegetation. He was led to undertake these 

 experiments, from having received a communication from Mr.Davies Gilbert, 

 in which he stated, that there was a district in Cornwall, where the soil 

 contained a large portion of arsenic; and that no plants could grow in it, 

 except some of the Leguminosse. By analysis, this soil yielded him about 

 50 per cent of arsenic, in the form of a sulphuret; the rest being composed 

 principally of sulphuret of iron, and a little silica. He had already ascer- 

 tained that a little of the sulphuret, mixed in soils, produced no injurious 

 effect on iS'inapis alba, barley, or beans; and that they flowered and seeded 

 freely when grown in it. Although the want of solubility in the sulphuret 

 might be assigned as a reason for its inactivity, yet it was certainly taken 

 up by water in small quantities, and imbibed by the roots of plants. Upon 

 watering them with a solution of arsenious acid, he found that they would 

 bear it in larger proportions than was presupposed. The injurious effect of 

 arsenious acid on vegetation, in the neighbourhood of the copper works of 

 Bristol and Swansea, was noticed by Mr, Rootsey; and Mi'. Stevens men- 

 tioned the circumstance of the trout, in some streams of Cornwall, having been 

 destroyed by the opening of some new mines in their neighbourhood, from 

 which arsenical compounds were discharged, though the vegetation did not 

 appear to be injured by them ; and it was fui'ther stated, that horses were 



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