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 Bushes 

 (fig. 78). There is little doubt, however, that these spaces 



FIG. 78. PORTION OF SECTION OF STEM OF RUSH, 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 



