110 VEGETABLE PHYSIOLOGY 
an upright position with comparatively little expendi- 
ture of material. A somewhat similar mechanism is met 
with in the stellate parenchyma of the stems of the Rushes 
(fig. 78). There is little doubt, however, that these spaces 
Fic. 78.—Porrion oF Section oF StEm or Rus#, SHOWING STELLATE 
TISSUE OF THE PITH, WITH LARGE INTERCELLULAR SPACES. 
are of great assistance in promoting the aeration of the 
whole structure. 
As has been already mentioned, the external orifices of 
the system of the intercellular spaces are the stomata of 
the leaves. In woody and corky parts these are supple- 
mented by the lenticels. The evidence for this statement 
does not consist only of microscopic examination of the 
