Infection by GLRaVs is limited to the phloem, (11) and results in the degeneration of primary phloem
tissues in shoots, leaves, and clusters.
In this portion, a pith begins to appear, and the primary xylem is spread into a continuous tangential ring and primary phloem
strands surrounding the pith (Figure 2B).
Internal to the cortex is the primary phloem fiber tissue, in which the principal fiber of interest is found, and immediately internal to this is the secondary phloem fiber tissue, a less desirable fiber generated by the cambium, the next discernible layer proceeding toward the stem center.
Selection for fiber has resulted in strains that have much more primary phloem fiber and much less woody core than encountered in narcotic strains, oilseed strains and wild plants.
The distribution of the phenolic and crystalliferous idioblasts, the circular arrangement of the primary phloem
, and the absence of metaxylem elements in the centre of the structure are also common among other species already described in the literature and have allowed identification of the adulteration of products being sold as sarsaparilla (Soares, 2013).
The provascular tissues give rise to the primary vascular system of the plant--the primary xylem and primary phloem. The cells of these tissues are highly specialized; xylem transports water and nutrients, whereas the phloem transports only organic solutes produced within the plant.
Primary phloem tissue is made up of sieve tube members, companion cells, fibers, and parenchyma.
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 (Figs.
Cell wall development was most pronounced in collenchyma, primary phloem
, and primary xylem vessels at the first sampling date, while other tissues such as epidermis, chlorenchyma, and pith parenchyma had only thin primary walls (Fig.
The primary phloem
bundles are also divided into four bundles (Figure 2F).
The presence of ribbed stems (7) and the occurrence of a cap of primary phloem
fibers (57) also support Cactoideae monophyly.
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.