THE TEANSPOET OF WATEE IN THE PLANT 75 



whose innermost layer, the endodermis, are often peculiarly 

 thickened, in much the same manner as those of the 

 exodermis already described (page 25). This thickening is not, 

 however, usually very marked in the region of absorption. 

 At certain places round the periphery of the stele of the root, 

 the woody strands (fig. 56, Sp) may be seen. These are in 

 contact with the succulent and turgid parenchyma which has 

 been filled with water in the way described, and consequently 

 the hydrostatic pressure which has thus been set up is'Jbrought 



Fiet. 56. SECTION OF ROOT, SHOWING ROOT-HAIRS ABUTTING ON THK 

 PARENCHYMA OF THE CORTEX, AND THE WOODY STRANDS, Sp, OF 

 THE STELE. (After Kny.) 



to bear upon the walls of the woody vessels which constitute 

 the greater part of those strands. These form the lower 

 portions of continuous open, or nearly open, tubes, which 

 extend from the roots to the leaves ; at the time when the 

 absorption of the root-hairs and cortex is greatest these 

 vessels are empty, or nearly so, and the effect of the hydro- 

 static pressure on their walls is to force the water from the 

 turgid cortex into the walls and cavities of the vessels. 

 How the water is distributed is not fully known ; we have 

 seen that lignified cell- walls have a certain power of taking 

 up water, and of passing it on with considerable rapidity, 

 so that part of it may be expected to remain in the walls. 

 Part, however, passes through into the cavities of the vessels, 



