TYPICAL VEGETABLE CELL. 49 



Vegetable cells are, on the average, not more than one five- 

 hundredth or one six-hundredth of an inch in diameter, though 

 in some cases they are large enough to be distinctly seen by the 

 unaided eye, as in the flesh of the Watermelon and the pith of 

 Elder ; in rare instances, as the internodal cells of Chara, they 

 may even be more than an inch long. Some cells, on the other 

 hand, are so small as to be barely visible under the highest 

 powers of the microscope, for example, some bacteria. 



The primary form of cells appears to be that of a sphere or 

 spheroid, but commonly, especially in the tissues of the higher 

 plants, they acquire forms quite different from this, and even 

 within the limits of the same organism the shapes may be ex- 

 ceedingly various. This may be due to mutual pressure, to 

 unequal growth caused by the unequal operation of various 

 physical forces, as gravitation, light, etc., or to other influence. 

 Cells, like the organs of which they are components, undergo 

 many modifications of form and structure, adapting them to 

 different uses. The cells which make up the body of a plant 

 are comparable to the human units which make up society. A 

 plant is a community or republic of cells, and, to understand it, 

 one must understand the individuals that compose it. 



TYPICAL VEGETABLE CELL. 



As all the different kinds of cells that go to make up the 

 various tissues of a plant are derived from cells that are at one 

 time all alike, we will begin by a consideration of these primi- 

 tive or typical cells, and afterwards study the various modi- 

 fications. 



Peel off the skin or epidermis from the convex surface of an 

 onion scale by making a cross incision and catching the skin 

 between the thumb and the knife or razor edge. Be careful not 

 to draw along with the epidermis any of the thick underlying 

 flesh of the scale. Mount a piece of the skin about a quarter- 

 inch square in water on a slide, cover carefully with a glass so 

 as not to include any air-bubbles. 



Examine with low power. Very little will be made out. 

 There is a fine and somewhat irregular network. This is due to 

 an aggregation in a single layer of a number of cells, the net- 

 work of lines being the bounding cell-walls, which are so nearly 

 transparent as to be almost invisible. If the light be properly 

 dimmed there may be seen in each cell a small denser-looking 

 body which is called the nucleus, and perhaps faintly granular 

 matter. The cells are filled with a semi-liquid matter, which, 

 however, is too transparent to be seen. 



Examine the various parts of a cell with high power. The 

 details are somewhat difficult to make out because of the trans- 

 parency of the cell contents. This is very often the case with 



