Sugarbeet Vasculature. I. Cambial Development and the Three-Dimensional Structure of the Vascular System

Using serial sections and cinematography, we studied vascular and successive cambial development and activity in sugarbeet plants grown in the phytotron and outdoors. Except for the first two leaves, which gave fewer veins, each leaf petiole has three major and several minor veins. Every leaf induces the formation of at least two cambial rings, eventually becoming directly connected with their secondary vascular tissues. The first cambium originates from procambium and interfascicular parenchyma, as in plants with one cambium. Fascicular cambia, which develop within traces of ca. four leaves, differentiate into one ring during the early stage of growth. Such a correlation was not found in mature beets. The leaf traces run across the stem to the periphery of the pith, anastomosing into different rings. All traces weave into a complicated network in the upper part of the hypocotyl, passing downward around the disintegrating pith and continuing into the rings of the root. In the root, a second cambium ring develops in the phloem parenchyma inside the endodermis. Each successive cambial ring differentiates in the outer parenchyma derivative already formed by a previous cambium. Radial connections between strands of adjacent rings and tangential connections between strands of the same ring are common. Cambia of successive rings are active simultaneously, each ring producing xylem and phloem at the beginning but mainly phloem later.