ROOTS AND THEIR RELATION TO PLANTS 21 



together with the minute sub-division of the epidermis from 

 which it springs (fig. 16, e), furnishes a good example of one 

 kind of plant cell. 1 Each live root hair consists of an ex- 

 tremely thin sac, the cell wall (shown in figs. 6 and 16 

 merely as a continuous line bounding the root hairs), and the 

 living contents of the cell, known as the protoplast. The cell 

 wall consists of a material known as cellulose, familiar to all 

 in the microscopic , , g 



fibers of cotton. The 

 cell contents, or pro- 

 toplast, of a root hair 

 consists largely of 

 a nearly transparent 

 portion, the cytoplasm, 

 composed of nitroge- 

 nous material which 

 may be roughly com- 

 pared to very thin 

 white of egg. Within 

 the cytoplasm are 

 found many some- 

 what opaque and 

 very minute particles, also rather large, clear spaces consist- 

 ing of very watery cell sap, and a structure less transparent 

 than the cytoplasm, known as the nucleus (fig. 16, ri). 



Other cells, of more complicated constitution than root 

 hairs, often contain many other structures and materials 

 besides those here mentioned. Some of these are briefly 

 discussed and figured in Chapter IV. 



18. The work of cells. The simplest plants, as will be shown 

 later, consist of a single cell each. Every ordinary flowering 



1 The student will find many illustrations of different types of cells in 

 later chapters. Some very simple ones are discussed in Chapter XV. Many 

 cells of the lower forms of plant life are much more easily studied than the 

 colorless and nearly transparent root hairs. The minute anatomy of the 

 cell is most easily studied in cells which exist as separate individuals and 

 which have among their contents some colored structures. 



FIG. 16. Cells from the surface of a young rootlet 



Showing epidermal cells (e) and one young and two 



older root hairs (h). In the root hairs the nucleus 



(n) and granular cytoplasm of the cells are shown. 



Greatly magnified. After Bonnier and Sablon 



