in regard to Earthy Matters. 175 



substance of the plant, supposing the salt to have been taken up 

 in the same ratio as the water. Now on burning the plant, and 

 examining its ashes, a trace of strontian certainly was detected, 

 but its whole amount did not reach the one-fifth of a grain, that 

 is, 2 per cent, of the whole quantity of earthy matter present, 

 my analysis indicating — Of lime, 7.30 grains ; strontian, 0.18 ; 

 total quantity of earth, 7.48. 



The conclusion to which I have been led by the foregoing ex- 

 periments may appear at first sight inconsistent with those de- 

 duced 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 ab- 

 sorbed 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 disor- 

 ganization which such bodies, by their presence, occasion in the 

 fibres of the roots. I have myself found that when a Pelargo- 

 nium had a portion of its roots immersed in a solution of bichro- 

 mate 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 excret- 

 ed by its roots ; and a similar result was obtained in the case of 

 another plant, in which a solution of proto-sulphate of iron had 

 been dissolved in the water in contact with its extremities.* 



But in all these instances the poisonous quality of the sub- 

 stance was evinced by the more or less rapid decay of the plant 



* That is to say, 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. 



