FOLIAGE LEAVES: FUNCTION, STRUCTUKE, ETC. 43 
FIG. 34. A hair from the leaf 
of Potentilla. It is seen 
to grow out from the epi- 
dermis. 
best protective substances (see Fig. 
32). Sometimes this cuticle be- 
comes so thick that the passage- 
ways through 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 epidermis. These 
may form but a slightly downy 
covering, or the leaf may be cov- 
ered by 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. 36). 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, 35). Sometimes, instead of a hair-like cover- 
ing, the epidermis develops scales of various patterns, 
often overlapping, and forming an excellent protection 
(see Fig. 37). In all these cases it should be remembered 
that these hairs and scales may serve other purposes also, 
as well as that of protection. 
36. Diminution 
of exposed surface. 
It will be impossible 
to give more than a 
few illustrations of 
this large subject. 
-r -i FIG. 35. A section through the leaf of bush clover 
I Very ary reglO (Lespedeza\ showing upper and lower epidermis, 
it has always been palisade cells, and cells of the spongy region. 
nntiVpr! tint flip The lower e P idermis Produces numerous hairs 
which bend sharply and lie along the leaf surface 
leaves are Small and (appressed), forming a close covering. 
