tem of the latter lower down. Now the next point to be clearly apprehended is that these vascular bundles of the leaves have the double duty of supporting the flattened
Fig. 22.—Sections across the leaf of oak. A. Slightly magnified and semi-diagrammatic, to show the general arrangement of the principal vascular bundles as seen cut across: m, midrib: e, marginal veins; s, lateral branches of midrib. Other smaller veins scattered between. B. A highly magnified vertical section of part of the above at a place free from vascular bundles: u, upper epidermis, with cuticle, c; p, palisade cells; ch, chlorophyll corpuscles, only drawn in a few cells; m, spongy tissue of mesophyll; i.s, intercellular passages communicating with the stoma, st, in the lower epidermis, l.
mass of leaf-tissue, and of carrying to and from its cells the water from the roots and the organic substances