80 



THE OAK. 



tern 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 prin- 

 cipal vascular bundles as seen cut across: m, midrib: , marginal 

 veins ; s, lateral branches of midrib. Other smaller veins scattered 

 oetween. B. A highly magnified vertical section of part of the 

 above at a place free from vascular bundles : , upper epidermis, with 

 cuticle, c; />, palisade cells; cA, chlorophyll corpuscles, only drawn 

 in a few cells; m, spongy tissue of mesophyll; .s, intercellular pas- 

 s-ages communicating with the stoma, st, in the lower epidermis, I. 



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

 the water from the roots and the organic substances 



