72 Plants and their Ways in South Africa 



To the outside of the xylem other cells of the bundle will 

 take the same stain as did those of the endodermis ; they also 

 contain starch and are in the part of the bundle called phloem 

 or bast. In this region sieve tubes occur. With a lens they 



cl — 



Fig. 71. — Stem of Helianthus (sunflower), cross section. Drawn by Miss 

 Averil Bottomley. E, Epidermis with hair {h), the outer thickened walls form 

 \.he. cuticle. C, Cortex. The outer cells with thickened angles form ^rc^/Z^wc^j^^a. 

 A resin gland (r) may be seen in the parenchyma. The innermost layer {e\ the 

 endodertnis or starch sheath, contains starch. S, Stele or central cylinder con- 

 taining one fibro- vascular bundle. {Pc), pericycle : it forms a cluster of scleren- 

 chymatous cells just outside each bundle. Between these cells and the bundle 

 cambium {fc) (fascicular cambium) lies the phloem. The portion of the bundle 

 inside the cambium is the xylem. It contains row^s of large thick-walled wood 

 vessels, (w) Medulla or pith, [ifc) Interfascicular cambium. 



can be made out by their larger size. Iodine stains their con- 

 tents, and those of neighbouring cells, yellow brown. 



Within the ring of bundles, the ground tissue making up 

 the greater portion of the stem is known as the medulla or pith, 

 and between the bundles the medullary rays extend out to the 

 cortex. They carry material from the wood out to the cortex 



