4 6 



present locally, and does not remain in one part when put there, 

 but permeates through the whole of the soil, and diffuses itself 

 equally. The soil then consists of minute angular fragments, 

 with gaps between them which are filled with air. 



Each solid particle of soil is surrounded by a film or layer of 

 water, held there by attraction — thick, if the soil be wet, thin, 

 if it be dry — and which we may artificially remove altogether. 

 The root-hairs wriggle their way among the particles, and come 

 into close contact with them, and with the moisture which adheres 

 to them. These root-hairs absorb water in the same manner as a 

 unicellular organism does, by virtue of the osmotic properties 

 of their cell-sap, which contains acids, and salts in solution. 

 The soil also possesses moisture containing salts in solution, but 

 in a very dilute solution, much less dense than in the cell-sap 

 of the plant itself. These are separated by a permeable mem- 

 brane, the cell-wall, and by the protoplasm, which, as we saw, 

 does not prevent the passage of a weak solution, but only pre- 

 vents the passage of a strong one. Accordingly, the previously 

 existing condition of equilibrium is broken, and the weak 

 solution passes into the cell-sap of the epidermal cell, while the 

 strong solution in the cell-sap cannot pass out in turn, because 

 of the restraining action of the protoplasm, so that a process of 

 endosmosis apparently takes place. Let us suppose the cell-sap, 

 in all the parenchyma cells intervening between the epidermis 

 and the central core, to have been originally of the same 

 strength. 



Parenchyma 

 Exterior Epidermal Cells Woody Core 



Epidermal Cells 











3 



The water taken up into the epidermal cell, by its hair-like 

 prolongation, from the soil has rendered its cell-sap weaker than 

 that of the parenchyma cell numbered ' I ' in the diagram; 

 consequently a process of endosmosis again goes on ; the cell- 

 sap of the cell ' i ' taking up water from the cell-sap of the 

 epidermal cell, until equilibrium is established between them, 

 and thereby becoming weaker in turn than the cell -sap of cell 



