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! 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 
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 eae 
Showing epidermal cells (e) and one young and two 
the cytoplasm are older root hairs (z). In the root hairs the nucleus 
found many some- (n) and granular cytoplasm of the cells are shown. 
Greatly magnified. After Bonnier and Sablon 
Fic. 16. Cells from the surface of a young rootlet 
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, n). 
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. 
