Longitudinal arrangement of leaf traces and compound vascular bundles in the stem of Aristolochia clematitis L.

Abstract

The compound vascular bundles in the Aristolochia clematitis stems are entirely composed of leaf traces. At the stage of protoxylem differentiation there is not one vessel in the compound vascular bundle which would belong solely to the stem. In a mature compound vascular bundle less xylem belongs to traces of higher lying leaves than to these of the lower situated ones. The lower ends of the particular traces, components of the compound vascular bundle, gradually become thinner. The traces of the upper leaves are represented in the xylem of the compound vascular bundle in the lower parts of the stem by several or even by only one metaxylem vessel. The latter constitutes a „trace" of the participation of the given leaf in the development of the compound vascular bundle. There are two categories of compound bundles in the stem. One part of these bundles does not reach to the stem apex and they develop on one side. They consist of halves (right and left) of traces of median lower leaves from one orthostichy. The others run uninterruptedly from the base to the stem tip and develop from the middle. They consist, namely, of the median traces (left or right) of lower leaves from the orthostichy and lateral leaf traces (left or right) from the second orthostichy.