70 VEGETABLE PHYSIOLOGY 



round the periphery of the stele of the root, the woody 

 strands (tig. 56, Sp) may be seen. These are in contact 

 with the succulent and turgid parenchyma which has been 

 tilled with water in the w r ay described, and consequently 

 the hydrostatic pressure which has thus been set up is 

 brought 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 



FIG. 56. SECTION OP BOOT, SHOWING ROOT-HAIRS ABUTTING ON THE PAREN- 

 CHYMA OP THE CORTEX, AND THE WOODY STRANDS, Sp, OF THE STELE. (After 

 Kny.) 



the hydrostatic 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, and in the early part of the 

 year, before the leaves of the plant expand, they thus 

 become filled with liquid. This filtration into the vessels 

 tends to relieve the pressure in the cortex, and additional 



