. A manual of botany. Botany. TISSUE SYSTEMS 343 stele. It is often found to contain sclerenchyma, either in isolated patches, or in the form of sheaths surrounding the vascular bundles (ficj. 728). The part of the stele within the pericycle may consist of a solid vascular cylinder containing no conjunctive tissue at all, or only a little dipping in from the pericycle in the intervals between the bundles, as in many roots. In Dicotj'ledons isolated vascular bundles sometimes occur in the pith. Where a large pith exists the cells of it tend after a time to break up and disappear, forming hollow
. A manual of botany. Botany. TISSUE SYSTEMS 343 stele. It is often found to contain sclerenchyma, either in isolated patches, or in the form of sheaths surrounding the vascular bundles (ficj. 728). The part of the stele within the pericycle may consist of a solid vascular cylinder containing no conjunctive tissue at all, or only a little dipping in from the pericycle in the intervals between the bundles, as in many roots. In Dicotj'ledons isolated vascular bundles sometimes occur in the pith. Where a large pith exists the cells of it tend after a time to break up and disappear, forming hollow stems as in the TJmhrUifcrce. These hollow stems are extreme instances of lysigenous formations. In polystelic stems each stele, in addition to its envelope of Fig. ..pe: pXi Fig. 729. Stele of stem of Feru, composed of three fused concentric bundles. PH. Endodermis. pp. Pericycle. ph. Phloem, px. Groups of protoxylem. endodermis, is surrounded by a layer of pericycle. Such steles are usually solid vascular tissue, and do not show intrastelar ground tissue, both pith and interfascicular ground tissue being absent {fig. 729). The Vascular Tissue System. • The Stele.—We have seen that the centre of the tissue of the growing point, which has been named the plerome, develops into a solid strand of complex character, forming the stele. Usually this remains single throughout the axis, and the plant is termed monostelic. The arrangements of its parts are different in the stem and the root, but there is a single central cylinder running throughout the whole axis. Separate 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 Green, J. Reynolds (Joseph Reynolds), 1848-1914. London, J. & A. Churchill
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