. The classification of flowering plants. Plants. 86 FLOWERING PLANTS [CH. uniform on both surfaces (fig. 25). The surface of the meso- phyll-cells in Finns is extended by infoldings of the walls (fig. 26). Resin-canals occur in definite positions in the mesophyll. A single bundle enters the leaf from the stem. In broader leaves it divides into several divergent strands. In narrow leaves there is a single median bundle-region bounded by a generally well-defined endodermis, within which is a single bundle or a pair of bundles surrounded by conjunctive tissue. The wood and bast are separated by
. The classification of flowering plants. Plants. 86 FLOWERING PLANTS [CH. uniform on both surfaces (fig. 25). The surface of the meso- phyll-cells in Finns is extended by infoldings of the walls (fig. 26). Resin-canals occur in definite positions in the mesophyll. A single bundle enters the leaf from the stem. In broader leaves it divides into several divergent strands. In narrow leaves there is a single median bundle-region bounded by a generally well-defined endodermis, within which is a single bundle or a pair of bundles surrounded by conjunctive tissue. The wood and bast are separated by a cambium-layer, which in the long-lived leaves adds to the tissues, chiefly in the form of phloem. The absence of a branched venation as a means of intercommunica- tion between the elements ^ ^^'d^^.^^A ^ of the bundle and the ing a comparison with the mesarch bundle of the leaves of Cycads. Certain points in the anatomy of the leaf have been found to be of value for systematic purposes, being constant in individual species but differing in allied ones. Such are the position and arrangement of the stomata, whether on the upper, or lower, or on both surfaces, whether in longitudinal bands, irregularly scattered, or confined to certain spots (their position is often indicated by a wax-secretion forming a glaucous bloom). The position, size, and, in a less degree, the number of the resin-canals is also of importance, as is also the simple or branched condition of the vascular bundle. The root consists at the growing-point of a central well- defined plerome surrounded by a many-layered periblem, the. mesophyll is partly balanced by an extension of the xylem by means of transfusion tracheides and of the phloem by albuminous cells. The former are developed chiefly on the side of the wood away from the bast, and Worsdell (see p. 52) has shewn some reason for supposing that they may be considered to represent a centripetal xylem, suggest- FiG. 26. Transverse section of leaf of Pinus L
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplants, bookyear1904
