Format: ORAL

Kishore S. Rajput

Department of Botany, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390002 (Gujarat) India

Migration of aquatic autophytes to terrestrial conditions compelled them to evolve a new strategy of specialised tissues for mechanical support and conduction i.e., secondary xylem and phloem respectively. From them, the phloem is a relatively delicate tissue that plays a vital role in the translocation of photosynthates. In most of the eudicots, the phloem develops external to the vascular cambium and the xylem internal to it. Besides their position external to the cambium, in a small fraction of eudicots, it also occurs within (interxylary phloem that develops from the single ring of vascular cambium) and inside (intraxylary) the secondary xylem. Based on their unique ontogeny, interxylary phloem is classified variously (Strychnos, Combretum, Azima and Calycopteris types) by earlier researchers. The present study documents several additional examples that do not fit into any of the types mentioned above (i.e., it develops in a later stage by dedifferentiation of parenchyma and not from the cambium). Similarly, the intraxylary phloem located on the pith margin either initiates from procambial derivatives, ground meristem, from the adjacent pith cells or by developing intraxylary cambium. Little information is available on the formation of intraxylary cambium and its unifacial (deposition of the secondary xylem and phloem in the same direction) or bifacial (xylem externally and phloem internally) nature but detailed information on its behaviour remains unexplored. Several such examples of intraxylary cambium with intermediate variants are also discussed herewith and their possible functions are attributed to defence against insect injury and herbivory based on pieces of experimental evidence available in the literature. Keywords: Intraxylary cambium, dedifferentiation, unifacial cambium, herbivory, internal phloem, included phloem, cambial variant