. Botany; an elementary text for schools. Plants. 260 STRUCTURE OF STEMS AND ROOTS arrangement of the bundles. The sections, if mounted in a permanent way, as in balsam, may be kept for further study of the bun- dles. Compare with Fig. 401. 422. EXOGENOUS STEMS.—The fibro-vas- cular bundles in exogenous (or dicotyledon- ous) stems are arranged in a circle around the center, which is usually filled with pith. Outside the ring of bundles is a cortex of fundamental tissue. Around this is either a layer of cork or an epidermis. Layers of parenchyma cells, called medullary rays, are found between t
. Botany; an elementary text for schools. Plants. 260 STRUCTURE OF STEMS AND ROOTS arrangement of the bundles. The sections, if mounted in a permanent way, as in balsam, may be kept for further study of the bun- dles. Compare with Fig. 401. 422. EXOGENOUS STEMS.—The fibro-vas- cular bundles in exogenous (or dicotyledon- ous) stems are arranged in a circle around the center, which is usually filled with pith. Outside the ring of bundles is a cortex of fundamental tissue. Around this is either a layer of cork or an epidermis. Layers of parenchyma cells, called medullary rays, are found between the bundles and often extend- '^^^^J'lhf course ing from the central pith to the outer cor- l{^^il°'i^^^tJ. tex. These cotyledons. usually are prominent in young stems of woody plants and in vines. Fig. 404. All trees and nearly all other woody plants of the temperate regions, as well as many herbaceous plants, show this plan of stem. The medullary rays are very prominent in oak wood. These rays are lignified in the xylem part of the bundle and non-lignified in the phloem part. To study arrangement of bundles in exogens: Pre- pare thin cross-sections of the stems of meni- spermum (moonseed),. 401. Fibro-vasciilar bundles of Indian corn, much magnified. A, annular vessel; a', annular or spiral vessel; XT', thick-walled vessels: W, tracheids or woody tissue; F, sheath of fibrous tissue surrounding the bundle; ft, fundamental tissue or pith; s, sieve tissue; p, sieve plate; c, companion cell; I, inter- cellular space, formed by tearing down of Adjacent cells; w', wood Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bailey, L. H. (Liberty Hyde), 1858-1954. New York, Macmillan Co.
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