The root hair absorbs water 

 from among the soil particles by 

 osmosis through the cell mem- 

 brane. In the cells near the sur- 

 face of the root, the proportion 

 of water molecules to other mole- 

 cules is greater than in the 

 deeper layers of cells, as we 

 should expect. Water in the 

 surface layers diffuses from cell 

 to cell, passing through several 

 cell membranes by osmosis. Sur- 

 rounding a live root hair there is 

 a constant flow of liquid 



OSMOSIS IN ROOTS 



Indeed, from what we know of the chemical activities of protoplasm, we 

 should expect materials to be passing into cells and out of cells by osmosis, 

 all the time. That is, tliere is a double current: (1) the protoplasm of a cell 

 receives from the outside its supply of water, salts and food; and (2) mate- 

 rials of various kinds pass out of the cell. Gases as well as liquids diffuse 

 through the wet cell wall. Every cell receives its income by osmosis, and it 

 gets rid of its wastes by osmosis. 



Osmosis in Living Things^ Some substances dissolve in water more 

 easily than others, and some solids do not dissolve at all. Substances in solu- 

 tion will diffuse, but not all will diffuse through a given membrane equally 

 fast. And through some membranes certain substances will not diffuse at 



i '4^%f^ 



L. v. I'lury, iluycu Thuinpson Institute 



PLASMOLYSIS IN EPIDERMAL CELLS OF RED CABBAGE 



When living plant or animal cells are placed in concentrated salt solution, the pro- 

 toplasm shrinks from the walls of the cells as water diflFuses out. An excess of fer- 

 tilizer makes a plant lose water through the roots and wilt 



^See No. 7, p. 95. 

 87 



