FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 87 



support and conduction are very perfect (see Fig. 27). It 

 is also clear that the green substance thus supported and 

 supplied with material is the important part of the leaf, the 

 part that demands the light-relation. Study the various 

 plans of the vein systems in Figs. 3, 9, 13, 18, 19, 20, 21, 

 25, 26, 51, 70, 75, 82, 83, 92. 161. 



Fig. 27. A plant (Fittonia) whose leaves show a network of veins, and also an adjust- 

 ment to one another to form a mosaic. 



30. Epidermis. — If a thick leaf be taken, such as that 

 of a hyacinth, it will be found possible to peel off from 

 its surface a delicate transparent skin {epidermis). This 

 epidermis completely covers the leaf, and generally shows 

 no green color. It is a protective covering, but at the same 

 time it must not completely shut off the green substance 

 beneath from the outside. It is found, therefore, that 

 three important parts of an ordinary foliage leaf are : (1) 



