FOLIAGE LEAVES: FUXCTION, STRUCTURE, ETC. 37 



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

 is also clear that tlie green substance thus supported and 

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

 part that demands the light-relation. Stud}' the various 

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

 25, 2U, 51, 70, 76, S2, S3, 92, 106. 



Fig. 2T. a plant (FUtonia) whose leaves show a network of veins, and also an aUjusl- 

 ment to one another to form a mosaic. 



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

 of a hya<'inth, 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 o-reen color. It is a protective covering, Init at the same 

 time it must not completely shut ofE the green substance 

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

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



