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A ray appears diagonally, from top left to bottom middle. Medullary rays , also known as vascular rays or pith rays , are cellular structures found in some species of wood . They appear as radial planar structures, perpendicular to the growth rings, which are visible to the naked eye.
Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In eudicotyledons, pith is located in the center of the stem. In monocotyledons, it extends only into roots. [1] The pith is encircled by a ring of xylem; the xylem, in turn, is encircled by a ring of phloem.
Parenchyma is a versatile ground tissue that generally constitutes the "filler" tissue in soft parts of plants. It forms, among other things, the cortex (outer region) and pith (central region) of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds.
During secondary growth, cells of medullary rays, in a line (as seen in section; in three dimensions, it is a sheet) between neighbouring vascular bundles, become meristematic and form new interfascicular cambium (between vascular bundles).
In a vascular plant, the stele is the central part of the root or stem [1] containing the tissues derived from the procambium. These include vascular tissue, in some cases ground tissue and a pericycle, which, if present, defines the outermost boundary of the stele.
The third wall is formed by ray cells, which are groups of radiating cells oriented perpendicularly to the stem axis, dividing the stem into segments not entirely unlike the slices of a pie. These groups of cells are not continuous and vary in length, height and thickness, forming a maze -like barrier to tangential spread of decay.
In anatomy, a medullary ray (Ferrein's pyramid) is the middle part of a cortical lobule (or renal lobule). Each consists of a group of nephrons in the renal cortex . [ 1 ] Their name is potentially misleading, as "medullary" refers to their destination, not their location.
This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology.