THE CELL. 



479 



stellate forms, by exclusive development of the free surfaces while the 

 contiguous cells remain attached at a few points, e. g. in cells of the paren- 

 chyma of leaves and leaf-stalks of many Monocotyledons (fig. 522), Musa, 

 Sagittaria (fig. 523), &c., and above all in the cellular tissue of Rushes 

 (fig. 524) and the steins of various aquatic plants. In the tissues of 

 Welwitschia, as also in Araucaria and other Conifers, very large irregu- 

 larly branching cells, covered with small crystals, may be seen : these are 

 sometimes called spicular cells. 



The mutual pressure of cells, commonly exerted in stems, in seeds, 

 hard parts of fruits, &c., converts the spheroidal into polygonal forms, of 



Fig. 526. 



Cells of the pith of Acanthus mollis, seen in a vertical section. Magn. 200 diam. 



which the more or less regular dodecahedron or tetradecahedron, giving an 

 hexagonal section, and arising from equal pressure in all directions, is 

 perhaps the commonest (pith of fully developed shoots of Dicotyledons, 

 such as Elder, &c.), or cubic, found in woodv fruits, &c. The cylindrical 

 becomes under the same circumstances prismatic, either six-sided with 

 flat ends, or with three rhombic faces at top and bottom, the common form 

 of the cellular tissue of the stems of herbaceous stems (fig. 526), or 4-sided 



