. The botany of crop plants : a text and reference book. Botany, Economic. STEMS 35 procambium strands. These three regions are best shown in a cross-section (Fig. 15). In a little older portion of the stem, such as shown in a section further back (Fig. 15), further differentiation has taken place, which changes involve the ground meristem and the procambium. The vascular bundle is composed of three re- gions: phloem, cambium and xylem. The center of the stem is made up of large, loosely fitting cells which constitute the pith or medulla. Radiating from the medulla out between the vascular bun
. The botany of crop plants : a text and reference book. Botany, Economic. STEMS 35 procambium strands. These three regions are best shown in a cross-section (Fig. 15). In a little older portion of the stem, such as shown in a section further back (Fig. 15), further differentiation has taken place, which changes involve the ground meristem and the procambium. The vascular bundle is composed of three re- gions: phloem, cambium and xylem. The center of the stem is made up of large, loosely fitting cells which constitute the pith or medulla. Radiating from the medulla out between the vascular bundles are a number of cells which make up the medullary ray. Dicot Vascular Bundle.âDe- tailed examination of a dicot vas- cular bundle in cross- and longitu- dinal sections shows each of its three parts to be made up of characteristic structural elements. Phloem.âIn the phloem are sieve tubes, companion cells, and phloem parenchyma. Each sieve tube is a single cell, much elon- gated and modified for conduc- tion. The end walls of sieve tubes (Fig. 16) are thickened, and per- forated by a great number of holes, and thus resemble a sieve. Each sieve tube is adjoined by a single row of small cells, the companion cells, which run parallel to it. Phloem parenchyma cells are somewhat. F â â (>â Fig. 16.âVascular elements. A, annular tracheal tube; B, spiral tracheal tube; C, reticu- lated tracheal tube; D, pitted tracheal tube; E, cross-section through plate of sieve tube, and adjoining companion cell; F, lengthwise section of sieve tube; G, portions of two com- panion cells. (£, F, and G after Strasbarger.). 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 Robbins, Wilfred William, 1884-1952. Philadelphia : P. Blakiston's Son
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