Elongation and Contraction of the Plant Axis and Development of Spongy Tissues in the Radish Tuber ('Raphanus sativus'L. cv. Saxa Nova)

摘要

The development of the tuber of Raphanus sativus L. cv. Saxa Nova is rather indefinite; morphologically this tuber is interpreted as a mass of tissue that is continuously remodelled. Strong elongation and contraction of upper half, lower half of the hypocotyl and the upper part of the taproot occur independently of each other and at different times of development. Elongation and contraction of these parts also vary enormously among individual plants. This behavior is evident in clay soil and in nutrient solution. When growing in clay soil, the lower half of the hypocotyl shows very strong elongation, while in nutrient solution, the upper half elongates the most. The radish tuber originates due to the activity of the vascular cambium in radial, tangential and in longitudinal direction (cambial secondary growth), but also due to the expanding and dividing of the xylem parenchyma cells (diffuse secondary growth). In healthy tubers all these meristematic activities occur completely in harmony with each other. As a result of elongation of part of the tuber axis the living elements in the secondary xylem expand and divide in longitudinal direction, including the phloem groups. (Copyright (c) Agricultural University Wageningen, The Netherlands, 1991.)