Plant anatomists are generally agreed on the histological products of successive cambia: bands of secondary phloem and associated secondary xylem (“vascular increments”) embedded in a background of conjunctive tissue (parenchyma, sometimes fibers). Interpretations have varied widely on the ontogeny of this plan. Studies have usually involved one or a few species. The study of numerous taxa, especially in centrospermoid families, leads to the conclusion that there is a common plan, although variations on it are manifold. A master cambium produces secondary cortex externally and, internally, rays, conjunctive tissue, vascular cambia, secondary phloem, and secondary xylem. Secondary phloem and secondary xylem are formed from the vascular cambium in each vascular increment. Vascular cambia function indefinitely, so that a master cambium and a series of vascular cambia (each in a vascular increment) function indefinitely. The master cambium either remains active as long as an axis is actively growing ...

https://bioone.org/journals/the-journal-of-the-torrey-botanical-society/volume-134/issue-2/1095-5674(2007)134[301:SCROHD]2.0.CO;2/Successive-cambia-revisited-ontogeny-histology-diversity-and-functional-significance/10.3159/1095-5674(2007)134[301:SCROHD]2.0.CO;2.pdf

Successive cambia revisited: ontogeny, histology, diversity, and functional significance

COSTEA, MIHAI (Department of Botany, University of Agronomical Sciences, Bucharest, Romania) and DARLEEN DEMASON (Botany and Plant Sciences, University of California, Riverside, CA 92521). Stem morphology and anatomy in Amaranthus L. (Amaranthaceae) taxonomic-significance. J. Torrey Bot. Soc. 128: 254-281. 2001.-The range of variation within the genus Amaranthus L. (Amaranthaceae) is described for a number of stem characters including: morphology, epidermis, primary stem vasculature and mechanism of secondary growth. The results provide new characters (phyllotaxy, complexity of leaf vascular supply and relative amount of secondary growth) that support (1) a new infrageneric classification (subgenus Amaranthus vs subgenus Albersia (Kunth)Gren. & Dodr.), and (2) the separation within the "hybridus" complex of cultivated amaranths (A. caudatus L., A. cruentus L. and A. hypochondriacus L.) from their presumed wild ancestors (A. hybridus L. subsp. quitensis (Kunth) Costea & Carretero, A. hybridus L. subsp. hybridus and A. powellii S. Wats. subsp. powellii respectively).

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Stem Morphology and Anatomy in Amaranthus L. ( Amaranthaceae )—Taxonomic Significance

Anatomical Adaptations of Halophytes

Successive cambia in liana stems of Paullinieae and their evolutionary significance in Sapindaceae

Secondary growth in the stem of Pupalia lappacea (L.) Juss. (Amaranthaceae) resulted in the development of successive rings of cambium. The cambium was storied, consisting only of fusiform cambial cells. Cessation of cell division in each cambial ring was followed by development of a new cambium from the outermost phloem parenchyma produced by the preceding cambium. Absence of ray cambial cells resulted in development of rayless secondary xylem and phloem. Development of conducting elements of xylem and phloem was restricted to the fascicular sector of cambial ring. Interfascicular sector of cambium gave rise to xylem fibres centripetally and axial parenchyma centrifugally. Xylem fibres retained their nucleus even after lignification of cell walls. Raylessness of the stem and possible significance of nucleated fibres are discussed.

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Structural and developmental studies on cambial variant in Pupalia lappacea (Amaranthaceae)

Phytolacca dioica (L.) is characterized by anomalous secondary thickening by means of supernumerary cambia. After a period of primary growth and the formation of an initial (normal) vascular cambium, supernumerary cambia are initiated outside of the primary vascular cylinder. The initiation of the first supernumerary cambium takes place through approximately the number of nodes equal to the denominator of the phyllotactic fraction characterizing a given axis. At each node a segment of supernumerary cambium is initiated opposite the leaf traces supplying the leaf inserted at that node. The segments of differentiated cambium arc preceded by regions of obliquely and antielinally dividing cells. In the single juvenile axis studied supernumerary cambial segments also appear above the node to the cathodic side of the entering leaf traces, and opposite the medullary bundle immediately anodic to these traces. Vascular eonnections among the primary and supernumerary vascular cylinders occur between leaf insertions on the same orthostiehy. The levels at which these connections oceur vary among stems. The switch from ordinary to anomalous secondary growth may be caused by a change in tissue response to stimuli produced by leaves.

Initiation and structure of the secondary vascular system in Phytolacca dioica (Phytolaccaceae)

Phytolacca dioica has a primary vascular system which includes medullary bundles. The primary structure of these bundles is composite, consisting of two to four collateral vascular strands with their phloem poles oriented toward a common center. A cambium is formed between the xylem and phloem of the strands and extends to enclose the phloem of the whole bundle. After a period of cambial activity the medullary bundles become amphivasal. As is typical of species with helieal phyllotaxy, the primary vascular system is organized into sympodia. The medullary bundles form the distal portions of the median leaf traces and continue in a medullary position for the number of nodes equal to the denominator of the phyllotactic fraction characterizing a given stem. As a medullary bundle passes out into a leaf, two or three vascular strands pass inward from the vascular cylinder to form a new medullary bundle. The number of medullary bundles in a stem is, thus, maintained. Variations of this pattern occur in the basal regions of juvenile shoots and in the basal and apical regions of adult flowering shoots. The relationship between leaf arrangement and the passing of vascular strand into the pith is discussed and a new classification of vascular systems with medullary bundles is proposed.

Abraham Fahn

Papers

Initiation and structure of the secondary vascular system in Phytolacca dioica (Phytolaccaceae)

The primary vascular system and medullary bundle structure of Phytolacca dioica (Phytolaccaceae)