CELL-CONTENTS AND FORMS OF CELLS. 263 



ference probably takes place mainly through the cortical and 

 medullary parenchyma, (rf) SPONGY PARENCHYMA, or loose, 

 spongy tissue with large intercellular spaces. The cells of this 



xf, 



FIG. 133. A cell from sassafras pith showing intercellular space (i); middle lamella 

 (m); layer of lignin (1); and layer of cellulose (c), which is subsequently modified to muci- 

 lage; simple pores (p) which are seen in the lower wall, the section being slightly oblique. 

 B, portion of wall showing the appearance of the pores when the view is transverse to the 

 wall and the focus is at the upper part of the pore (a) or at the lower part (b). 



type vary from slightly branched cells, as in the mesophyll of 

 leaves, to those which are strongly branched and stellate, as in 

 Juncus, Pondederia, and the stems of various marsh plants. In 



