VII] OF STELLATE CELLS 547 



matically by the pith of the banana. The cells are stellate, and 

 the tissue has the appearance in section of a network of six-rayed 

 stars (Fig. 211), linked together by the tips of the rays, and separated 

 by symmetrical, air-filled intercellular spaces, which give its snow- 

 like whiteness to the pith. In thick sections, the solid twelve-rayed 

 " star-dodecahedra " may be very beautifully seen under the 

 binocular microscope. They are not difficult to understand. 

 Imagine, as before, a system of equal spheres in close contact, each 

 one touching its twelve neighbours, six of them in the equatorial 



Fig. 211. Stellate cells in pith of Juncus. 



plane ; and let the cells be not only in contact, but become attached 

 at the points of contact. Then, instead of each cell expanding so 

 as to encroach on and fill up the intercellular spaces, let each tend 

 to shrink or shrivel up by the withdrawal of fluid from its interior. 

 The result will be to enlarge the intercellular spaces ; the attachments 

 of each cell to its neighbours will remain fixed, but the walls between 

 these points of attachment will be withdrawn in a symmetrical 

 fashion towards the centre. As the final result w^e have the star- 

 dodecahedron, which appears in plane section as a six-rayed figure. 

 It is necessary not only that the pith-cells should be attached to 

 one another, but also that the outermost should be attached to a 

 boundary wall, to preserve the symmetry of the system. What 



