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.jpg)
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
