STRUCTURE OF THE PRIMARY SHOOT OF EPHEDRA-VIRIDIS COV

The internodal vasculature in Ephedra viridis Cov. consists of eight v ascular bundles: four leaf traces and four axial bundles. In the nodal plexus, the four leaf traces diverge into the leaves, two per leaf. A s they continue upward, the axial bundles on either side of the stem f use for a short distance and then separate. Above this level, but stil l in the nodal region, the four axial bundles divide, giving rise to f our small branch traces, which diverge into the branches, two per bran ch. Above the node, each of the four axial bundles divides again, rees tablishing eight vascular bundles in the internode. The chlorophyllous leaf intergrades from an isobilateral to a weakly bifacial appearance , tip to base. The two collateral veins of the leaf consist entirely o f primary phloem and primary xylem and are bordered by poorly defined bundle sheaths, which are interrupted by transfusion tracheids and gel atinous fibers. Notable features of the node are the presence of the n odal plexus, relatively short cell lengths, numerous transfusion trach eids, and collenchymatously thickened parenchyma cells. The latter occ ur in the pith and interfascicular regions. In the internode, four to five layers of cortical chlorenchyma are radially arranged around the vascular cylinder. The internodal bundles are composed of primary phlo em and primary xylem separated by the precursors of the fascicular cam bium. Transfusion tracheids, parenchyma cells, and fibers make up the interfascicular regions. The interfascicular cambium originates in cel ls bordering already established fascicular cambia and spreads lateral ly. The transition to secondary growth begins in the node and spreads basipetally. The cambial activity of the first year produces secondary phloem and secondary xylem in the bundles, but only secondary xylem i n the interfascicular regions. The secondary vascular tissue of the fi rst year lacks rays.