Stem anatomy at various developmental stages of secondary growth in Turbina corymbosa (Convolvulaceae)
Methods – Several samples of the stem with various diameters were studied using a histological method. Morphological and anatomical analyses were carried out using light microscopy.
Key results – With the initiation of secondary growth, stems lose their circular outline rapidly due to unequal deposition of secondary xylem and formation of successive cambia. New successive cambia initiate from parenchymatous cells as small crescent-shaped fragments on asymmetric/opposite sides and result in a different stem conformation. Though several segments of successive cambia are formed, very few stem samples form complete cambium rings. The secondary xylem formed by successive cambia is diffuse porous with indistinct growth rings and is composed of both wide and narrow (fibriform) vessels, tracheids, fibres, axial and ray parenchyma cells. The secondary phloem consists of sieve tube elements, companion cells, axial and ray parenchyma cells. In fully grown plants, cambial action (internal cambium) occurrs between the intraxylary phloem and protoxylem and produces secondary xylem and phloem near the pith region.
Conclusion – Structural alterations and unequal deposition of conducting elements, occurrence of intraxylary phloem and flattening of the stem are suggested to facilitate rapid growth of the plants by providing required minerals and nutrients. Internal cambium formed at the periphery of the pith is bidirectional and produces secondary xylem externally and intraxylary phloem internally. Continued development of intraxylary phloem from the internal cambium provides an additional path for rapid and safe translocation of photosynthates.
Keywords: CAMBIAL VARIANT; CHRISTMAS VINE; INTERNAL CAMBIUM; INTRAXYLARY PHLOEM; SECONDARY XYLEM AND PHLOEM; SUCCESSIVE CAMBIA
Document Type: Regular Paper
Publication date: August 22, 2018
Plant Ecology and Evolution (a continuation of Belgian Journal of Botany, incorporating Systematics and Geography of Plants) is an international journal devoted to ecology, phylogenetics and systematics of all ‘plant' groups in the traditional sense (including algae, cyanobacteria, fungi, myxomycetes), also covering related fields such as comparative and developmental morphology, conservation biology, evolution, phytogeography, pollen and spores, population biology, and vegetation studies. It is published by Meise Botanic Garden and the Royal Botanical Society of Belgium and contains original research papers, review articles, checklists, short communications and book reviews.
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