18 A LABORATORY MANUAL OF BOTANY 
Note the very fine veins running through all spaces between 
larger veins. The normally green tissue through which the 
veins run is called the mesophyll, the internal part of the 
leaf. Draw, showing the skeleton of the leaf. 
From both surfaces of some of the leaves remove the 
epidermis by carefully peeling it away with the scalpel. 
Mount it with the outside up and examine with the low 
power of the microscope. Note the form of the epidermal 
cells. Note also pairs of crescent-shaped cells with an 
opening between them. The opening extends well into 
the mesophyll. 
The pair of cells, called guard-cells, and the opening be- 
tween are called a stoma, often spoken of as a “ breathing- 
pore.” Note the distribution of stomata throughout the 
epidermis. Does the epidermis from both leaf surfaces con- 
tain stomata? Draw stomata and some of the epidermal 
cells. 
General suggestions.—The structures seen in these les- 
sons are all concerned in enabling the plant to live. The 
root-hairs take up water from the soil and it passes through 
the roots into the stem, and from the stem most of it goes 
into the branches and leaves. In the roots, stem, branches, 
and leaves the water passes through woody tissue, which is 
especially arranged for this work. We see this tissue in the 
leaves as the veins, and in the stems _and roots it makes 
up the strong woody cylinder. The plants that persist for 
a period of years (perennials) have much more of a woody 
cylinder than plants growing but a single season (annuals). 
In the water taken up by the root-hairs are numerous 
substances that are essential to the proper sustenance of 
plants, and in order to obtain sufficient quantities of these 
substances more water is taken up than is really needed. 
Consequently the surplus water must be disposed of, and 
this is done mainly through the stomata. If stomata are 
examined when the plant has too much water they will be 
