protoxylem


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Related to protoxylem: metaxylem

protoxylem

[¦prōd·ō′zī·ləm]
(botany)
The part of the primary xylem that differentiates from the procambium and is formed during elongation of an embryonic plant organ.
References in periodicals archive ?
Passage cells are usually aligned with protoxylem poles (Fleet 1961, Peterson & Enstone 1996), so the flow of water through them is more intense and efficient than through the other cells.
secundum, nine protoxylem poles were observed, different from the description of Oliveira & Sajo (1999a), that registered 17 protoxylem poles for this species.
11b) tend to be collateral, with protoxylem (px) internal to the central phloem strand, but metaxylem (mx) external to it.
In most monocots, however, there is probably no cellulosic network in the primary walls of protoxylem (Carlquist & Schneider, 2011), as illustrated by grasses.
For Sculthorpe (1967), the ample protoxylem lacunae observed in the vascular bundles of the seven species may represent the only structure that transports water for many aquatic species.
There are usually three (rarely four) protoxylem points with central
They have narrow phloem strands adjacent to large, single, permanent protoxylem or metaxylem elements.
These changes are: #20, quadriseriate branching of axes/leaves absent [right arrow] throughout; #28, stele with radiating arms of xylem absent [right arrow] as rounded lobes; #41, radial axis/rachis trace round-elliptical [right arrow] lobed; #46, position of protoxylem in rachis/axis toward no face [right arrow] toward several faces; and #88, exospore surface nearly smooth or plain [right arrow] obviously sculptured.
Examples of such structural synapomorphies for the extant Cycadales are girdling leaf traces, an inverted omega pattern of vascular bundle arrangement in petiole and cataphyll bases, protoxylem poles changing from endarch in the stem to exarch in the leaf traces, a primary thickening meristem, a contractile taproot, and ageotropic, coralloid, lateral roots (Stevenson, 1990b; Norstog & Nicholls, 1998).
The lateral roots are initiated as single, enlarged endodermal cells opposite the protoxylem poles of the main root tip.