482 Royal Society. 
By George Rainey, Esq., M.R.C.S. Communicated by P. M. Roget, 
M.D., F.R.S. 
The ascent of the sap in vegetables has been generally ascribed 
to a vital contraction either of the vessels or of the cells of the plant : 
the circumstances of that ascent taking place chiefly at certain sea- 
sons of the year, and of the quantity of fluid, and the velocity of its 
motion being proportional to the development of those parts whose 
functions are obviously vital, as the leaves and flowers, have been 
regarded as conclusive against the truth of all theories which pro- 
fessed to explain the phenomenon on purely mechanical principles. 
The aim of the author, in the present paper, is to show that these 
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 mereury. 
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 inte 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, . 
