Functional (water-conducting) tracheary elements of all anthesis flower parts, including the pedicel, had helical bands and thus were part of the primary xylem
microstructure, with examples from Zingiberales.
Are there monocots in which primary xylem and early metaxylem are vesselless but metaxylem contains vessels?
The studies of Bierhorst and Zamora (1965) show that in families and species from 165 angiosperms (including basal angiosperms, sensu APG III, 2009), primary xylem contains vessels in all of the species they studied.
The roots were either diarch with two primary xylem
strands or triarch with three primary xylem
strands cleaving into two or three wide secondary xylem lobes.
The primary vasculature is non-sympodial, and primary xylem
only occurs as the downward extension of mesarch leaf traces (Fig.
For example, "It should be noted in passing that the phylogenetic transitions between tapered and truncated vessel members may be considerably accelerated in the primary xylem particularly in the case of helically thickened, tracheary elements.
1944) and others have suggested complex scenarios that involve "primitive" characters being retained in primary xylem and the first-produced secondary xylem.
Torus-bearing pit membranes are present in secondary xylem (wood) and largely or completely absent from primary xylem
diversifolia has a peripheral ring of 24-36 collateraL vascular bundles each with a conspicuous crescent-shaped bundle cap and a strip of densely stained cambial cells between the primary phloem and the primary xylem