Formation of medullary phloem in Argyreia nervosa (Burm. f.) Bojer

Kilas K Kapadane,Ravindra A Shelke,Amit D Gondaliya,Kishore S Rajput

doi:10.14719/pst.2019.6.2.498

Kilas K Kapadane, Ravindra A Shelke + Show 2 more

Open Access

https://doi.org/10.14719/pst.2019.6.2.498

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Abstract

Histologically, family Convolvulaceae is characterised by the presence of successive cambia, medullary (internal/intraxylary) and interxylary phloem in majority of the species, whereas some of the members are devoid of successive cambia and medullary bundles. The present study on Argyreia nervosa (Burm. f.) Bojer showed the presence of medullary bundles while internal phloem was absent during the primary growth. As the secondary growth progressed, successive cambia initiated from the pericyclic parenchyma. Development of medullary bundles began along with the regular protoxylem and protophloem while formation of intraxylary phloem was observed only after the initiation of secondary growth. Medullary/intraxylary sieve elements began to develop from the marginal pith cells. In thick stems, small segments of internal cambium initiated between the protoxylem and internal phloem. This internal cambium was functionally unidirectional and produced internal phloem centripetally. Developmental particulars are described in details along with its significance.

Highlights

Climbing habit in the family Convolvulaceae has evolved with various kinds of cambial variants such as successive cambia, internal cambium, successive internal cambia, functionally inverse cambium, interxylary, intraxylary phloem, medullary bundles etc. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
Occurrence of above-mentioned anatomical features are common throughout the family except presence of medullary bundles in the Convolvulaceae is reported in Argyreia nervosa by Pant and Bhatnagar [10] and in A. nervosa and A. roxburghii by Govil [19]
Stem anatomy: Thick stems of fully grown Argyreia nervosa were composed of several successive rings of secondary xylem alternating with phloem (Fig. 1A)

Summary

Introduction

Climbing habit in the family Convolvulaceae has evolved with various kinds of cambial variants such as successive cambia, internal cambium, successive internal cambia, functionally inverse cambium, interxylary (included phloem), intraxylary (internal) phloem, medullary bundles etc. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. Horizon e-Publishing Group of medullary bundles in A. nervosa is reported earlier by Pant and Bhatnagar [10] and Govil [10,19]. According to them these bundles may be conjoint, collateral, bicollateral, semi concentric, concentric, amphivasal, amphicrible or obcollateral with well-developed phloem. Medullary bundles undergo secondary thickening due to the cell division activity of the cambium present between the xylem and phloem [10]. They were explored in detail composition of medullary bundles and their types in A. nervosa. Number of medullary bundles may vary from species to species and age of the of the same species

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