THE SEED 5 
ing membrane which contains a living substance called 
protoplasm. This is the essential part of the cell, and, so 
far as we know at present, the physical basis of all life. 
Cells are commonly more or less rounded in shape, though 
they take different forms according to the purpose they 
serve. Sometimes, as in the fibers of cotton and the down 
of young leaves, they are long and hairlike; when closely 
packed, they often become angular by pressure, like those 
shown in Figs. 10,11. The cells composing the thick body of 
the bean are for the most part starch and other substances 
stored up for food, which render observation difficult. It 
will, therefore, be better to choose for a study of the indi- 
vidual cell some kind that will show the essential parte more 
distinctly. 
7. Microscopic examination of a cell.— Place under a high 
power of the microscope a portion of fresh skin from one of 
the inside scales of an onion, or a piece 
of the root tip of a very young corn or oat 
seedling, and fix your attention on one of 
the individual cells. Notice (1) the cell 
wall or inclosing membrane, w (Fig. 11) ; 
(2) the protoplasm, p, which may be 
recognized by its granular appearance ; 
(83) the nucleus, n; and (4) the cell sap, s. 
In very young cells the protoplasm will 
be seen to fill most of the interior; but 
2 : Fic. 11.—Typical cells: 
in mature ones, like the large one on the ™, nucleus ; 9, protoplasm ; 
w, cell wall; s, sap. 
right of the figure, it forms a thin lining 
around the wall, with the nucleus on one side, while the cell 
sap, composed of various substances in solution, occupies the 
central portion. Though there is generally an inclosing wall, 
this is not essential, its office being to give strength and me- 
chanical support by holding the contents together, as an 
India-rubber bag holds water. It is the turgidity of the cell, 
when distended with liquid, that gives firmness to herba- 
ceous plants and the tender parts of woody ones. This 
