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 ; e, 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, 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 epider- 

 mis, I. 



mass of leaf-tissue, and of carrying to and from its cells 

 the water from the roots and the organic substances 



