26 A TEXT-BOOK OF BOTANY 
(3) The cuticle, which is often developed upon the 
epidermis, is one of the best protections against loss of 
water. It is developed by the exposed walls of the epi- 
dermal cells, and being constantly renewed from beneath it 
may become very thick and many-layered (Fig. 19). Some- 
times the cuticle be- 
comes sothick that the 
passageways through 
it to the stomata re- 
semble tubes (Fig. 20). 
In dry regions, or in 
Fic. 21.—Section through the leaf of bush clover, 
showing upper and lower epidermis, palisade @NY much exposed 
cells, and cells of the spongy tissue; the lower place, the cuticle is a 
epidermis produces numerous simple hairs that 
bend sharply and lie along the surface of the Very constant feature 
ii of plants. 
(4) Havrs in great variety are developed upon leaf 
surfaces, being outgrowths from the epidermal cells. They 
may form only a slightly downy covering (Fig. 21), or the 
leaf may be covered by a woolly 
or felt-like mass so that the epi- 
dermis is entirely concealed, as 
in the common mullein (lig. 22). 
In dry or cold regions the hairy 
covering of leaves is very notice- 
able, often giving them a brilliant 
silky white or bronze look. Some- 
times instead of hairs the epi- 
dermis develops scales of various 
patterns (Fig. 23), often overlap- 
ping and forming a complete 
covering. The great variety of 
these hairs and scales, and the 
ease with which they may be ex- 
amined, make them an attractive study. At the same 
time, just how they protect the leaves is by no means 
Fic. 22.—Branching hair of 
mullein. 
