80 THE OAK 
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 mag- 
nified and semi-diagrammatic, to show the general 
arrangement of the principal vascular bundles as seen 
cut across; m, midrib; ¢, marginal veins; s, lateral 
branches of midrib. Other smaller veins scattered be- 
tween. B. A highly magnified vertical section of part 
of the above at a place free from vascular bundles: 
u, upper epidermis, with cuticle, ¢; 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 epider- 
mis, J. 
mass of leaf-tissue, and of carrying to and from its cells 
the water from the roots and the organic substances 
