Fusiform initials – produce elongated cells such as the Tracheids, vessel elements, and fibers of the xylem, as well as the sieve tube members, companion cells, parenchyma, and fibers of the phloem; fusiform ends and are oriented parallel to axis of a stem/root Ray initials – shorter and oriented perpendicular to stem or root axis, produce vascular rays—radial files consisting mainly of parenchyma cells; move water and nutrients between secondary xylem and secondary phloem Xylem ray – portion of vascular ray located in secondary xylem Phloem ray – portion of vascular ray located in secondary phloem Heartwood – as tree or woody shrub ages, the older layers of secondary xylem no longer transport water and minerals; they are closer to the center of a stem or root Sapwood – outer layers still transport xylem sap Only the youngest secondary phloem, closest to the vascular cambium functions in sugar transport. As a stem or root increases in circumference, the older secondary phloem is sloughed off, which is why secondary phloem does not accumulate as extensively as secondary xylem Suberin – waxy material in cork cells that makes stem or root impermeable to water and gases Lenticels – dot the Periderm, small raised areas; more space between cork cells enabling living cells within a woody stem or root to exchange gases with the outside air Leaves arise from nodes; roots do not Epidermis forms on the exterior of the leaf, and vascular tissue in the interior
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