292 



NATURE AND PEOPEETIES OF SOILS 



pendently. The absorption of mitrients by plants, in its 

 simplest analysis, is but a working out of this phenomenon. 

 Thus, if the concentrations of K"^ ions is high in the soil 

 solution and low within the cell, the potassium will move 

 inward in response to diffusion forces, providing, of course, 

 the ions can pass through the cell wall. This penetration is 

 entirely independent of the entrance of water, as far as the 



,D» 





Fig. 51. — Left, wheat seedling with 

 soil particles clinging to root-hairs. 

 Above, root-hairs much enlarged. 

 Root-hairs are simple tuhe-like pro- 

 longations of the border cells. 



movement of the latter is concerned. Moreover, the equaliza- 

 tion of one ion is more or less unrelated to the concentration 

 equilibrium of any other. The osmosis of the water, on the 

 other hand, is a phenomenon dependent on sum-total concen- 

 tration plus the semi-permeable membrane. 



154. Differential diflfusion. — The intake of nutrients is 

 by no means as simple as the above explanation might lead one 

 to assume, due to the complications interposed by the presence 

 of a semi-permeable membrane. The passage of ions and mole- 

 cules through the cell-wall and the protoplasmic membrane 



