CELL-CONTENTS AND FORMS OF CELLS. 265 



with reference to the other, and which enable it to withstand 

 undue strain and pressure. There are two principal forms, namely, 

 (a) collenchyma and (b) sclerenchyma. 



The collenchyma cell is elongated, prismatic, with soft 



Fig. I3S. A, cells of endosperm of the seed of the date palm (Phccnix dactylifera) , the 

 one normal and the other showing the stratification of the wall after treatment with 

 chlor-zinc-iodide. 



B, cell of endosperm oi Phytelephas macrocarpa (vegetable ivory) showing lamellation 

 and spherite structure in the wall after treatment with chlor-zinc-iodide, clove oil, chromic 

 acid or certain other reagents. 



C, cell of endosperm of Strychnos Nux-vomica after treatment with iodine and potas- 

 sium iodide solution. 



D, opposite pores in the walls in contiguous cells of vegetable ivory showing striae 

 between them after treatment with iodine solution. 



Walls consisting mainly of cellulose and never lignified ; the contents 

 being rich in water. In transverse section it is readily distin- 

 guished by the local thickening of the walls, i.e., at the angles of 



