THE VEGETABLE CELL. 75 



fluids, ill which the open orifices of a cut stem dip, to ascend in 

 its vessels. 



At first sight it seems very easy to give an explanation of the 

 ascent of the sap, both before the opening of the buds at the re- 

 commencement of vegetation, as well as during the period in 

 which the plants are clothed with leaves. DuriDg the period of 

 the rest of vegetation, the cells of a perennial plant are filled with 

 a great quantity of organic compounds, under the form of proteine 

 substances, sugar, gum, and more paiticularly of starch, which 

 latter is converted into sugar at the re-commencement of vegeta- 

 tion. In consequence of this, the cell-sap becomes capable of 

 setting up a powerful endosmose, and nothing seems more natural 

 than that the cells of the roots should absorb the water which 

 exists around them, and that the sap diluted by this should 

 be taken up by the cells above, and so be carried gradually up- 

 wards from one cell to another, whence the notion that endosmose 

 is the sole and sufficient cause of the motion of the sap, counts 

 many adherents even in recent times. But on closer examination 

 the matter appears less simple than it seemed at the first glance. 

 The organic compounds, especially the starch, are not, for the 

 most j)ai t, contained in the elongated cells of the wood, in which 

 the sap ascends, but more particularly in the cells of the me- 

 dullary rays and in those of the rind of the root, while in those 

 Monocotyledons, which, like the Palms, lay up a store of sugar, 

 gum, starch, &c., before the time of flowering, these substances 

 are deposited in the parenchymatous cells of the stem. Thus the 

 substances which cause the setting up of the endosmose, occur in 

 cells which do not preside over the conveyance of the sap, while 

 in the elongated cells of the wood, substances which would cause 

 endosmose exist only in inconsiderable quantity, and in the ves- 

 sels not at all. How then does the sap reach the wood -cells and 

 vessels, and how is its motion imparted to it? I consider these 

 questions as unsolved at present, 



Briicke (1. c. 204) has indeed promised to demonstrate that this 

 process depends on the laws of endosmose, that the parenchyma- 

 tous cells first become densely filled with water by the help of the 

 soluble and expansible substances contained within them, and 

 then since they continually attract water, pour out that which 

 they cannot make room for in their cavities, with a portion of the 

 soluble substances, as sap, into the neighbouring vessels; but 

 Briicke has not yet furnished the demonstration of this. But 

 even if we would assume such an excretion from the cells causing 

 the endosmose, to be founded on the laws of that phenomenon, it 

 still would remain unexplained why this emptying of the paren- 

 chymatous cells does not take place by the most dii^eet path, into 

 the intercellular passages running between them, but into the 

 wood-cells and vessels. 



The influence which the leaves exert upon the ascent of the sap, 



