THE CELLULAR CONSTRUCTION OF THE PLANT 



21 



multiply by division. None of these constituent parts of the cell are 

 known to he evei' produced de novo, but are always, like the plant itself, 

 the descendants of progenitors of like nature. It is different with the 

 cell-wall. In cell-division it appears as a new film deposited from 

 the protoplasm, while, as we shall see, it may be absent altogether 

 from reproductive cells. It is thus a body of secondary importance, 

 as compared with the more constant constituents of the cell. 



DlFFEREXTI.-\TIOX OF TiSSUES. 



Passing in the examination of the longitudinal section of any 

 bud from the growing point downwards, successively older tissues 



Fig. 12. 

 Parenchyma-celU from the cortex of the root of FriliUaria : longitudinal section 

 ( X 550). A, very young cells, not yet vacuolated. B, older cells vnth numerous 

 vacuoles containing cell sap, s, each surrounded by the protoplasm, p. C, older cells, 

 mth larger vacuoles filled with sap, s. The protoplasm (p) Unes the cell-walls 

 internally, and embeds the nuclei (A), which may be suspended centrally, or placed 

 laterally. The large eel! to the left has a single large central vacuole, or cell- 

 cavity. (.\fter Sachs.) 



