SKCTION 16.] ANATOMICAL STRUCTURE. 



131 



solid matters and in age mos^y air naturally came to be named a CELL. 

 Bat the name was suggested by, and first used only for, cells in combination 

 or built up into a fabric, much as a wall is built of bricks, that is, into a 



401. Cellular Structure or Tissue. Suppose numerous cells like 

 those of Fig. 437 to be heaped up like a pile of cannon-balls, and as they 

 grew, to be compacted together while soft and yielding ; they would flatten 

 where they touched, and each sphere, 

 being touched by twelve surrounding 

 ones would become twelve-sided. Kg. 

 438 would represent one of them. 

 Suppose the contiguous faces to be 

 united into one wall or partition be- 

 tween adjacent cavities, and a cellular 

 structure would be formed, like that 

 shown in Fig. 439. Roots, stems, leaves, 

 and the whole of phan- 

 erogamous plants are a 

 fabric of countless num- 

 bers of such cells. No 

 such exact regularity in 

 size and shape is ever 

 actually found ; but a nearly truthful magnified view of a small portion of 

 a slice of the flower-stalk of a Calla Lily (Fig. 440) shows a fairly corres- 



ponding structure ; except that, owing to the great air-spaces of the interior, 

 the fabric may be likened rather to a stack of chimneys than to a solid 

 fabric. In young and partly transparent parts one may discern the cel- 

 lular structure by looking down directly on the surface, as of a form- 

 ing root. (Fig. 82, 441, 442). 



402. The substance of which cell-walls are mainly composed is called 

 CELLULOSE. It is essentially the same in the stem of a delicate leaf or 

 petal and in the wood of an Oak, except that in the latter the walls are 



FIQ. 438. Diagram of a vegetable cell, such as it would be if when spherical it 

 were equally pressed by similar surrounding cells in a heap. 



FIG. 439. Ideal construction of cellular tissue so formed, in section. 



FIG. 440. Magnified view of a portion of a transverse slice of stem of Callt 

 Lilv. The great spaces are tubular air-channels built up bv the cell*. 



