34 
THE VEGETATIVE FUNCTIONS OF PLANTS 
them to the eye, 1 in order to examine opaque objects, 
sections of them must be cut, thin enough to be readily 
transparent. The conditions of observation are also 
much simplified by this means. 
Thin cross-sections of leaves, that is, sections cut at 
right angles to the surface, are readily made with a sharp 
FIG. 27. Cross-sections of leaves of an oak (Quercits novimexicana), 
showing the effect of different light conditions on the internal anatomy. 
I. from leaf growing in sunlight; 2, from leaf growing in the shade. (After 
Clements.) 
razor. When examined with the microscope, such sections 
disclose a structure similar to that illustrated in Fig. 27. 
The epidermis, both upper and lower, is seen to consist 
of a single layer of cells. The free surface of the outer 
cell-wall is coated with a layer of a wax-like substance, 
1 Objects examined with the unaided eye are observed with light re- 
flected from their surface to the eye. 
