FOLIAGE LEAVES : FCXCTIOX, STRUCTURE, ETC. 43 



Fig. 34. A h.air from the leaf 

 of PotentiUa. It is seen 

 to grow out from the epi- 

 dermis. 



best protective substances (see Fig. 

 'i'i). Sometimes this cuticle be- 

 comes so tliicli that tlie passage- 

 ways tlirongli it leading down to 

 the stomata become regular canals 

 (see Fig. 33). 



Another very common protective 

 structure upon leaves is to be found 

 in the great variety of hairs de- 

 veloped by the ejiidermis. These 

 may form but a slightly downv 

 covering, or the leaf may be cov- 

 ered liy a woolly or felt-like mass 

 so that the epidermis is entirely 

 concealed. The common mullein 

 is a good illustration of a felt- 

 covered leaf (see Fig. 30). In cold 

 or dry regions the hairy covering 

 of leaves is very noticeable, often 

 giving them a brilliant silky white or bronze look (see 

 Figs. 34. 3.5). Sometimes, instead of a hair-like cover- 

 ing, the epidermis develops scales of various patterns,, 

 often overlapping, and forming an excellent protection 

 (see Fig. 3T). In all these cases it should be remembered 

 that these hairs and scales may serve other purpioses also, 

 as well as that of protection. 

 3(i. DimiEution 



of exposed surface. — 



It will be impossible 

 to give moi'c than a 

 few illustrations of 

 this large subject. 

 In very dry regions 

 it lias always been 

 noticed that the 

 leaves are small and 



Fig. 35, A section tiirough the leaf of bush clover 

 (Ltsptdeza'), showing upper aud lower epidermis, 

 palisade cells, and cells of the spongy region. 

 The lower epidermis produces numerous hairs 

 which bend sharply and lie along the leaf surface 

 tappressedX forming a close covering. 



