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Inner wall of epidermic cells are thin; parenchyma composed of polyhedral cells; collateral bundles with a set of sclerenchyma fibers are located at the periphery, each collateral bundle includes two lateral strands of phloem, a central bundle composed of small strands of phloem surrounded with phloematic fibers, a large vessel of metaxylem, several small vessels of protoxylem and xylematic parenchyma.
However, Souza (2009), who examined seedlings of other eudicots, found that primary roots may present from two (diarch) to five (pentarch) protoxylem poles.
3) In any given organ of a vessel-bearing monocot, metaxylem vessels show more "specialization" than those in protoxylem, and late metaxylem is more specialized than early metaxylem.
Thus the element on the lower right is protoxylem and the pitted element to its upper left, metaxylem.
Number variation of protoxylem poles may occur among species (EAMES; MacDANIELS, 1953) and along of a seedling primary root (SOUZA, 2009).
1930): "In view of the proof offered that the transition from the protoxylem to the secondary xylem represents a primitive to specialized sequence which is palingenetic, and the accurate portrayal this sequence gives the change from scalariform to porous perforations, there is little reason to doubt that the detailed transitions here illustrated give a connected picture of the evolution of the scalarifiorm vessel segment from the scalariform tracheid" (1930, pp.
The inhibition in vascular system development and the collapse of protoxylem cells of young galls, in general, could happen in function of cell hypertrophy and tissue hyperplasia, as proposed by Souza et al.
This study compares the anatomical structure, the diameter of vascular bundles (metaxylem, protoxylem, and the sheath of sclerenchyma), the diameter and number of fibers of the sheath, and the classification type sensu Weiner and Liese (1990, 1993) as well as the number of cells in each field of view for the fundamental parenchyma taken from the central cylinder of stems of D.