in.] BOTANY. II 



usually of a very thin and transparent membrane, 

 which may contain air only, when the cells are dead 

 (as in pith) ; or a fluid, as in the cells of orange-pulp ; 

 or, besides fluid, granules of protoplasm (Par. n), 

 coloured by substances which are green in leaves, and 

 of other tints in many flowers; or granules of starch. 

 Sometimes the cell-wall is very thick and hard, as in 

 the stone of the cherry and other stone-fruits, and the 

 leathery surface of leaves such as those of the stone- 



FIG 3. Thick- walled cells from a leaf of stone-pine as seen in a cross-cut, 

 many times the real size. 



pine (Fig. 3). Some plants are formed wholly of 

 cellular tissue (mosses, fungi, seaweeds, lichens), and 

 almost all plants have more cellular than any other 

 tissue. Fluids can pass through the walls of the cells, 

 and the nourishment which is sucked up by the roots 

 in the fluid state, is distributed through the plant chiefly 

 by passing from cell to cell. The celte which cover 

 the surface of the plant are a good deal flattened, and 

 form a layer called the epidermis. 



7. Wood-tissue, of which in addition to vessels 



