116 



VEGETABLE PHYSIOLOGY 



construction. The hollow stems with n 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 



FIG. 78. PORTION OF SECTION OF STEM OF HUSH, SHOWING STELLATE 

 TISSUE OF THE PITH, WITH LARGE INTERCELLULAR SPACES. 



with in the stellate parenchyma of the stems of the Bushes 

 (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 



