433 



objections are not valid, and to prove, by a series of experiments, 

 that the motion of the sap is totally independent of any vital con- 

 tractions of the passages which transmit it ; that it is wholly a mecha- 

 nical process, resulting entirely from the operation of endosmose ; 

 and that it takes place even through those parts of a plant which 

 have been totally deprived of their vitality. 



The lower extremity of a branch of Valeriana rubra was placed, 

 soon after being gathered, into a solution of bichloride of mercury. 

 In a few hours a considerable quantity of this solution was absorbed, 

 and the whole plant, which had been previously somewhat shrunk 

 from the evaporation of its moisture, recovered its healthy appear- 

 ance. On the next day, although the lower portion of the branch had 

 lost its vitality, the leaves and all the parts of the plant into which 

 no bichloride had entered, but only the water of the solution, were 

 perfectly healthy and filled with sap. On each of the following days 

 additional portions of the stem became affected in succession ; but 

 the unaffected parts still preserved their healthy appearance, and 

 the flowers and leaves developed themselves as if the plant had ve- 

 getated in pure water and the whole stem had been in its natural 

 healthy state. On a minute examination it was found that calomel, 

 in the form of a white substance, had been deposited on the internal 

 surface of the cuticle ; but no bichloride of mercury could be de- 

 tected in those parts which had retained their vitality ; thus showing 

 that the solution of the bichloride had been decomposed into chlo- 

 rine, calomel, and water, and had destroyed the vitality of the parts 

 where this action had taken place ; after which, fresh portions of the 

 solution had passed through the substance of the poisoned parts, as 

 if they had been inorganic canals. Various experiments of a similar 

 kind were made on other plants, and the same conclusions were de- 

 duced from them. 



As the addition of a solution of iodide of potassium converts the 

 bichloride of mercury into an insoluble biniodide, the author was 

 enabled, by the application of this test to thin sections of the stems 

 of plants into which the bichloride had been received by absorption, 

 to ascertain, with the aid of the microscope, the particular portion 

 of the structure into which the latter had penetrated. The result 

 of his observations was, that the biniodide is found only in the in- 

 tercellular and intervascular spaces, none appearing to be contained 

 within the cavities of either cells or vessels. 



As the fluids contained in the vessels and in the cells hold in so- 

 lution various vegetable compounds, their density is greater than 

 the ascending sap, which is external to them, and from which they 

 are separated by an intervening organized membrane. Such being 

 the conditions requisite for the operation of the principle of endos- 

 mose, the author infers that such a principle is constantly in action 

 in living plants ; and that it is the cause of the continual transmis- 

 sion of fluids from the intervascular and intercellular spaces into the 

 interior of the vessels and cells, and also of the ascent of the sap. 



