In the root and collet region, each primary xylem bundle breaks into a median protoxylem and a pair of metaxylems, and in this portion a pith begins to appear (Figure 2E, F).
Development patterns in stem primary xylem of woody Ranales.
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.
This idea was enunciated by Bailey (1944) who thought of the primary xylem as a refuge for "primitive" xylem characteristics in woody angiosperms.
Five basic cell types make up the primary xylem: vessel, elements, tracheids, fibers, and parenchyma.
The parenchymal cells associated with primary xylem function for storage and synthesis of certain metabolites.
Vascular cambium activity in primary xylem
was intense; the fusiform initials were long, radially flattened and tangentially tapering with overlapping ends.
vessels were all lignified at the youngest maturity stage sampled.
Central cylinder (Figure 5A) shows on the periphery groups of not lignified fibers, primary phloem and scarce secondary, cambium, reduced amount of secondary xylem, and primary xylem
. There is pith of parenchymatic nature with secretory ducts (Figure 5A).
Torus-bearing pit membranes are present in secondary xylem (wood) and largely or completely absent from primary xylem
. Some pit membranes containing elongate rather than circular tori are the result of fusion of adjacent pits during ontogeny.
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
Central cylinder is composed of uniseriate parenchymatous pericycle and three strands of primary xylem
and phloem (Figure 2A and B).