. Plants; a text-book of botany. Botany. FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 43. Fig. 34. A hair from the leaf of Poteniilla. It 16 seen to grow out from the epi- dermis. best protective substances (see Fig. o2). Sometimes this cuticle be- comes so thick th;it the passage- ways through it leading clown to the stomata become regular canals (see Fig. 33). Another very common protective structure ujjon leaves is to be found in the great variety of hairs de- veloi)cd by the ejsidermis. These may form but a slightly downy covering, or the leaf may be cov- ered by a woolly or felt-like mass so
. Plants; a text-book of botany. Botany. FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 43. Fig. 34. A hair from the leaf of Poteniilla. It 16 seen to grow out from the epi- dermis. best protective substances (see Fig. o2). Sometimes this cuticle be- comes so thick th;it the passage- ways through it leading clown to the stomata become regular canals (see Fig. 33). Another very common protective structure ujjon leaves is to be found in the great variety of hairs de- veloi)cd by the ejsidermis. 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. 3(j). 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, ;)). 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 rememliered 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. In very dry regions it lias always been noticed tliat the leaves are small and. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Coulter, John Merle, 1851-1928. New York, D. Appleton and company
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