Effects of the Particle Size and Moisture Content of Soil on the Number of Vascular Bundles in the Roots of Tobacco Seedlings

Abstract

In order to make clear the effect of particle size and moisture content of soil upon the number of vascular bundles in the primary roots of tobacco, the 27∼50 day's seedlings of the variety Bright Yellow which had been grown in the nursery bed, were transplanted to the pots with the soil of various sizes of sand particles and various soil moisture contents ranging from 30 to 100%. Afterwards, the number of vascular bundles in the primary roots developed from the main ones were measured. The result of the experiment revealed that the number of vascular bundles in the primary roots increases with the decreasing size of soil particles and with increasing soil humidity and, furthermore, that the vascular numbers have an intimate correlation with the diameter of the roots. Variability of vascular numbers has a connection with the position of the primary roots on the main ones, namely, the primary roots form higher positions bear more vascular bundles than those from the lower ones. Differential diffusion of air and dissolved oxygen due to different particle sizes and soil humidities will designate the branching at corresponding positions on the main roots and, moreover, the number of vascular bundles in the developing primary roots.