ACTION OF PiOOT-HATRS 



41^ 



temperature till its interstices are apparently empty be exposed 

 to a heat approaching that of boiling water, a considerable 

 quantity of vapour will be given off, due to the volatilising of the 

 hygroscopic films. 



We have seen that the youngest roots and rootlets are 

 furnished near their apices with a number of delicate hairs ( fifl. 

 1181) or outgrowths of their epidermal cells {fig. 1182), which 

 make their way into the interstices of the soil. Not only do 

 these play a very important part in anchoring the plant to the 

 substratum, but they are the means by which the water is 

 absorbed. The delicate walls of these root-hairs come into the 

 closest relationship to the particles of soil.pressmg in some cases 



Fig. 1181. 



Fig. 1182. 



FUi. 1181. Ultimate branches of a root, show- 

 ing position of root-hairs. Fig. 1182. 



Root-liairs on the surface of a vounsr root. 



SO closely upon them, that the particles are embedded in the 

 membrane. The hygroscopic film of water is so separated from 

 the interior of the root-hair by a most delicate pellicle of almost 

 pure cellulose. The cell-sap in the hair contains a certain 

 amount of acid in solution, and by vhtue of this osmosis is set 

 up. The root-hairs, which are very numerous, become turgid, 

 and by continued osmosis the water is passed inwards to the 

 cortex of the root, all the cells of which soon exhibit considerable 

 turgescence, thus causing a great deal of hj'drostatic pressure 

 in the cortex. AX the places where the latter abuts upon the 

 xylem elements of the stele a filtration under this pressure takes 

 place, so that the water is forced into the axial woody tissue. 



VOL. II, E E 



