116 VEGETABLE PHYSIOLOGY 
construction, The hollow stems with a rigid periphery, 
strengthened at intervals by diaphragms, such as occur at 
the nodes of these organs, are especially adapted to main- 
tain an upright position with comparatively little expendi- 
ture of material. A somewhat similar mechanism is met 
‘e. 
Se 
Fic. 78.—Porrion or SEcTion of Srem or Rusu, sHowiNG STELLATE 
TIssuUE OF THE PiTH, witH LAargE INTERCELLULAR SPAcEs. 
with in the stellate parenchyma of the stems of the Rushes 
(fig..78). There is little doubt, however, that these 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 
