Occurrence of rayless secondary xylem in some Indian herbaceous species

Abstract

(Received 28 December 2000 and in revised form 26 February 2001) Absence of rays was observed in the secondary xylem of thirteen species from seven genera of Aizoaceae, Chenopodiaceae, and Polygonaceae. Among the species studied, all the members of Polygonaceae had normal secondary xylem, whereas in Aizoaceae and Chenopodiaceae the vascular cylinder of the mature stem was composed of successive rings of xylem alternating with phloem bands. All the species of Chenopodiaceae and Polygonaceae accumulated scanty secondary xylem composed of vessels, tracheids, libriform fibers, and axial parenchyma, while in Aizoaceae, in addition to the above-mentioned cell types, fibriform vessels and fiber tracheids were also observed. In the latter part of secondary growth in both Chenopodium species, some of the axial parenchyma underwent transverse division and formed a group of vertically elongated, procumbent cells, referred to here as pedomorphic rays. In all species studied, nuclei were retained in the lumen of xylem...