Plants and their ways in South Africa . ath. Surrounded by the endodermis lies the stele. It consistsof a mass of ground tissue or conjunctive tissue withinwhich lies a broken ring of tissue forming elliptical patches.In a fresh stem they appear white toward the centre andgreenish without. These are the complex fibro-vascularbundles. Iodine has stained the inner portion a reddishbrown. This region, the xylem, contains the wood vesselsand fibres. If the stem which was placed in methyl blue beexamined it will be seen that these cells have taken up the bluesince they serve for the upward path of
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Plants and their ways in South Africa . ath. Surrounded by the endodermis lies the stele. It consistsof a mass of ground tissue or conjunctive tissue withinwhich lies a broken ring of tissue forming elliptical patches.In a fresh stem they appear white toward the centre andgreenish without. These are the complex fibro-vascularbundles. Iodine has stained the inner portion a reddishbrown. This region, the xylem, contains the wood vesselsand fibres. If the stem which was placed in methyl blue beexamined it will be seen that these cells have taken up the bluesince they serve for the upward path of the transpirationcurrent. ^This stain does not injure the stem, a few grains should be dissolvedin water until the solution is a clear bright blue. 71 72 Plants and their Ways in South Africa To the outside of the xylem other cells of the bundle willtake the same stain as did those of the endodermis; they alsocontain starch and are in the part of the bundle called phloemor bast. In this region sieve tubes occur. With a lens they cl —. Fig. 71.—Stem of Helianthus (sunflower), cross section. Drawn by MissAveril 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 theendodertnis 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 bundlecambium {fc) (fascicular cambium) lies the phloem. The portion of the bundleinside the cambium is the xylem. It contains row^s of large thick-walled woodvessels, (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 upthe greater portion of the st