70 VEGETABLE PHYSIOLOGY 
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 
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 
Fic. 56.—Srction or Root, sHowInG Roov-HaIRS ABUTTING ON THE 
PaRENCHYMA OF THE CoRTEX, AND THE Woopy Srranps, Sp, oF 
THE Steve. (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 
