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After the initiation of the secondary growth, sclereids are also formed in the secondary phloem (Fig.
Laticifers was described from secondary phloem samples of the trunk by were fixed in Karnovsky solution (Karnovsky, 1965), dehydrated in 50, 70 and 80% alcohol, embedded in HistoResin (hydroxyethylmethacrylate; Leica, Germany), following the manufacturer's instructions, and cut in a semiautomatic microtome.
13) were constituted only by bark, that is, periderm and secondary phloem (Fig.
These cylinders of intensive mitotic activity give rise to secondary growth: tissues laid down toward the center of the plant become the secondary xylem, and those laid down toward the outside of the plant become the secondary phloem. Both tissues arise from the same single layer of cells, and no one is quite sure what causes one daughter cell to become xylem and another phloem.
This is immediately followed by differentiation into an inner strip of secondary xylem and an outer strip of secondary phloem tissues.
Compensating for this minimal-strength configuration is the secondary phloem which has prominent bands of phloem fibers (Fig.
Anatomical descriptions of secondary phloem structures (Esau 1965, Fahn, 1990), revisions of their nomenclature and directions for the description of these tissues (Trokenbrodt 1990, Junikka 1994), as well as a proposal of classification based on their anatomical features (Furuno 1990) have been published.
The primary cell walls of most stem tissues (chlorenchyma, cambium, secondary phloem, xylem fibers and vessels, and parenchyma) were thin walled and did not thicken during maturation (Engels and Jung, 1998).
No fibers have been reported in the secondary xylem, but the secondary phloem is rich in fibers (accounting for the fact that some xylarium samples consist entirely or mostly of secondary phloem).
Secondary phloem. Each vascular cambium in a species with successive cambia is capable of producing more secondary phloem (1sp, Fig.
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.