7 ~E TEANSPOET OF WATEE IN THE PLANT 69 



the Jm of hygroscopic water which surrounds them. In 

 so- Ceases the pressure between the two is so close that 

 t 1 .rticles become embedded in the membrane (fig. 55). 

 r l . -^groscopic film of water is thus separated from the 

 ; of the root-hair by a most delicate pellicle of cell- 

 bstance, lined by an almost equally delicate layer of 

 ism. The vacuole of the hair contains a somewhat 

 U.-sap, by virtue of which osmosis is set up; the 

 {equivalent of the acids of the 

 ; considerable, the cell quickly 

 turgid and distended, such 

 -e continuing so long as the 

 remain favourable. The root- 

 ^ry numerous, and their united 

 'jies a considerable accumula- 

 fr in the cortex of the root, 

 "_, into the cells of this region 

 ^rough the base of the hair. 



mtt ;.: 

 wall 

 prot< 

 acid v 

 osmot 

 sap be ; 

 become' , 

 turgea 

 conditi 

 hairs ar 

 action c 

 tion of w 

 for it pas 

 by osmosi, 



This, beinj; )0ne of the cells of the ex- 

 ternal layei. i impinges upon one or more 

 of the cortifa cells, which have a similar 

 reaction tc ;/at of the root-hair itself. 

 Osmotic CL v\nts are thus set up from 

 every hair, ^ a gradual accumulation 

 of water tak, - place in the cortex of the 

 young root, r making all its cells turgescent and causing 

 a considerably [^hydrostatic pressure in the tissue. This 

 turgescence ^ ( ith its consequent pressure extends all along 

 the axis of th< ^ung root, though it is originally set up only 

 by the region ^hich is clothed by the absorbing hairs. 



The central portion of the axis of the root is occupied 

 by a cylindrie /, mass which extends throughout its whole 

 length, and wi,ieh is known as the stele (fig. 56). It is 

 generally mark-jd off sharply from the cortex, the cells of 

 whose innermost layer, the endodermis, are often peculiarly 

 thickened. This thickening is not, however, usually very 

 marked in the region of absorption. At certain places 



FIG. 55. ROOT-HAIR 

 IN CONTACT WITH 

 PABTICLES OF SOIL. 



