162 STRUCTURAL BOTANY 



instead of vessels (cf. p. 66). The bundles are 

 accompanied by thin - walled parenchyma, and the 

 whole strand, bundle and parenchyma together, is 

 enclosed by a well-marked sheath of cells containing 

 abundant starch (see Fig. 63). The parenchyma 

 accompanying the bundles is continuous with that of 

 the central cylinder of the stem, and it is through this 

 tissue that the sugar formed in the leaf passes down 



FIG. 63. Part of transverse section of foliage-leaf of White 

 Lily, e, epidermis ; s, stoma ; p.p palisade paren- 

 chyma ; s.p, spongy parenchyma ; v. b, vascular bundle, 

 with xylem above and phloem below. Magnified 

 about 70. (U.S.) 



towards the bulb, to be there formed into a store of 

 starch. * 



In this leaf, as in most horizontal leaves, we find 

 that there is a marked difference between the upper 

 and lower parts of the ground-tissue ; in fact, we have 

 here, as in the Wallflower, to distinguish between 

 palisade and spongy tissue. The palisade cells, 

 however, are of a peculiar form (see Fig. 63, p.p) ; 

 they are branched, and the branches (two or three to 

 each cell) are placed at right angles to the surface of 



