. A textbook of botany for colleges and universities ... Botany. the so-called Fig. 937. — A cross sec- tion through a leaf of the fragrant olive {Osmanthus fragrans), showing a T- shaped sclereid {s), which to- gether with the thick cuticle (c) accounts for the stiffness of the leaf; note the three palisade layers (p), indicat- ing relative xerophytism; highly magnified. As noted elsewhere, the cutinized outer epidermal wall is an important means of stiffening in these and other leaves, supplemented in some cases by a thickening of the lateral epidermal walls (as in Ficus, fig.
. A textbook of botany for colleges and universities ... Botany. the so-called Fig. 937. — A cross sec- tion through a leaf of the fragrant olive {Osmanthus fragrans), showing a T- shaped sclereid {s), which to- gether with the thick cuticle (c) accounts for the stiffness of the leaf; note the three palisade layers (p), indicat- ing relative xerophytism; highly magnified. As noted elsewhere, the cutinized outer epidermal wall is an important means of stiffening in these and other leaves, supplemented in some cases by a thickening of the lateral epidermal walls (as in Ficus, fig. 801) or even of the hypodermal walls (as in Pinus, fig. 1039). In the leaves of xerophytic grasses and sedges, patches of thick-walled bast fibers and other mechanical cells may occur just beneath the epidermis (fig. 835), and festoons of such cells often surround the conductive bundles, giving a great amount of strength to the leaves. Some- times (as in Osmanthus, fig. 937) evergreen leaves con- tain isolated mechanical cells (sdereids) extending from the lower to the upper epidermis, apparently acting as supports or braces; occasionally these stiff cells are Y- or T-shaped. The outer cortical layers of most petioles have the collenchymatic thickening charac- teristic of young stems (p. 697). The tearing of leaves at their margins is prevented largely by the presence there of an extra amount of cutinization, while similar protection is afforded in many leaves by marginal veins. Lobed leaves would seem especially subject to tearing at their sinuses; in some cases (as in Ribes, fig. 938) strong arcuate veins Fig. 938.—A portion of a leaf of the golden currant (Ribes aureum), showing ar- cuate veins (v) just below the leaf sinuses, where the danger of tearing otherwise would be 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 per
Size: 1369px × 1825px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
