THE FUNCTIONS OF ROOT-HAIRS. 51 



These, and numerous other experiments of the 

 same kind, prove that the healthy root-hair is a 

 h'ving instrument for taking up dilute solutions 

 out of the soil, and holding them in the sap- 

 cavity for a time. If killed, by frost for instance, 

 it loses these powers. 



The researches of the last ten years have also 

 shown that a time comes when the turgid cell, 

 if an isolated one, and if sufficient supplies of 

 water are present, is so tightly distended that the 

 surplus water begins to diffuse out again under 

 the pressure proper to the hydrostatic conditions 

 set up. 



Now we arrive at a very critical point. 



When the water, or dilute solution of various 

 substances, begins to exude under pressure from 

 the living root-hair, what is to prevent its escape 

 into the soil ? And if it thus diffuses out, where 

 is the object of absorption ? 



The questions are obviously pertinent, and they 

 may seem the more so in that the cells adjoining 

 the root-hair on its inner side are also turgid, 

 and possess similar properties to those of the 

 root-hairs. To establish a condition of things 

 which shall bring about the inward flow of the 

 absorbed water, one of the three following cases is 

 conceivable. (i) The cells, as we pass radially 

 into the root, have different properties on the 

 wall of the two sides ; or (2) they are more 

 and more greedy of water owing to some process 

 of extraction of their water by tissues in the 

 centre of the root ; or (3) these successive series 



