Miscellaneous. 135 



not a pure and simple absorption of the solution, but a double cur- 

 rent is formed. As the salt of the solution passes into the plant, so 

 the salts of the plant arrive in the solution. This is the principle 

 which M. Dutrochet has so well developed in his excellent investi- 

 gations on Endosmosis. 



There is a strong and a weak current, but always a double current, 

 and not a pure and simple absorption. This cause of error is very- 

 important, for Theodore de Saussure operated only upon 637 mil- 

 ligrammes, diminished by the fact of the absorption alone, and he 

 did not at all attempt, in his analyses, as may be seen at page 255 

 of his * Recherches sur la Vegetation,' to find any other principles 

 than those which he wished to estimate ; moreover he has not indi- 

 cated the weight of the plants he employed. 



To avoid, as far as possible, the chances of error caused by the 

 excretions of the roots, I thought that plants should be chosen which, 

 living a considerable time in water, might, by a very long vegeta- 

 tion, be brought into such a condition as no longer to yield any 

 fixed salt to the distilled water, and which would yet possess a 

 marked power of absorption. Mentha aquatica seemed, from nume- 

 rous previous experiments, to fulfil these conditions much better 

 than the Polygonum persicaria and Bidens cannabina, selected by 

 Theodore de Saussure. The following is the manner in which my 

 experiments were made. Branches of mint, furnished with nume- 

 rous adventitious roots, which had lived in pure water for more than 

 six months, were placed in flasks containing distilled water which 

 was renewed every five days. When the reagents did not indicate 

 any foreign salt in this water, I made with these plants precisely the 

 same experiments as Theodore de Saussure had done, and I then 

 found, that a vegetable freely immersed by its roots in a very dilute 

 solution of several salts, having no chemical action on its tissues, 

 absorbs all the substances contained in that solution in equal pro- 

 portions. 



The differences which I have pointed out in my memoir, in the 

 absorption of substances contained in one and the same solution, are 

 too slight for us to admit, with Theodore de Saussure, that the roots 

 select certain salts in a solution in preference to others : that he ar- 

 rived at different conclusions, results from his having operated only 

 on a few centigrammes of salts in solution, and having omitted to 

 take into account the excretion which is continually going on from 

 the roots simultaneously with the absorption. 



The differences observed in analysing the residue of the solutions 

 depend on certain salts being fixed in the plants, either from their 

 concurring in the development of special organs, as the phosphates 

 to that of the grain of the grasses, or from their forming insoluble 

 combinations with some principles of the plant j whilst other sub- 

 stances, which are not subjected to either of these two conditions, 

 are excreted freely by the roots : thus it appears to me that the in- 

 verse of Theodore de Saussure's conclusion is correct. 



Roots which are immersed in water absorb indifferently all the 

 substances dissolved in this liquid ; but the excretions, on the con- 

 trary, may present great differences. — Comptes Rendus, June 8, 



