. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. OLD AND YOUNG LEAVES. 353 the sun and wind. The ribs themselves are composed of cellular structures which are not open to the danger of over-transpiration, and the epidermis which covers them is entirely devoid of stomata. When the leaves at the ends of the young twigs are opposite, erect, and concave, and their margins are in contact, they form an actual capsule round the apex of the shoot. This occurs in the Wayfaring Tree (Viburnum Lantana), illustrated in fig. 905. The small folds of green tissue
. The natural history of plants, their forms, growth, reproduction, and distribution;. Botany. OLD AND YOUNG LEAVES. 353 the sun and wind. The ribs themselves are composed of cellular structures which are not open to the danger of over-transpiration, and the epidermis which covers them is entirely devoid of stomata. When the leaves at the ends of the young twigs are opposite, erect, and concave, and their margins are in contact, they form an actual capsule round the apex of the shoot. This occurs in the Wayfaring Tree (Viburnum Lantana), illustrated in fig. 905. The small folds of green tissue project into the interior of the capsule, and the still closely-pressed lateral veins form the outer wall, and at the same time furnish a protective covering for the enlarging green portions of the leaf. As soon as these are fully developed, and the. Fig. 92.—Unfolding of Beech-leaves, 1 The brown bud-scales have been loosened, and the membraneous stipules surrounding the foliage-leaves are visible above. 2 Further stage of development, the folded foliage-leaves being visible between the stipules. 8 The same twig further developed. * lower surface of a young folded leaf. s Portion of the same leaf; the depressions caused by the folding are bridged over by silky hairs. « Surface view of an unfolded leaf; the stipules are withered and about to fall. * Vertical section of a leaf at right angles to the midrib. 8 Vertical section parallel with the midrib. epidermal cells are correspondingly thickened, the projecting folds become smooth, the veins separate from one another, and the whole leaf becomes flat, assumes a horizontal instead of a vertical position, and turns the upper instead of the lower surface to the incident light (see fig. 90 6). It has already been repeatedly stated that coats of varnish as protective coverings are especially to be met with on young leaves, which they guard from over-transpiration and desiccation during their development, and that when the leaf-la
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
