Histological Analysis of the Thickness of Rice Roots

Abstract

The relationships .between the thickness of rice (Oryza sativa L.) roots in their diameters and the quantitative characteristics of the component tissues were investigated microscopically. The results obtained were as follows. 1. The increasing curves of the thickness of the root and the component tissues in the root tips were found to fit to an allometric formulae as shown in Fig. 2. The distance from the apex to the thickness-establishing level of whole root was 500∼1500μ, which was responsible to that of the thickness-establishing level of the cortex. On the other hand, the stele diameter was established at a more apical level. 2. There were highly positive correlations between the root diameter and the quantitative characters of the component tissues with the exception of metaxylem vessel. (Table 2). 3. The regression of the thickness of cortex parenchyma on the root diameter was observed to be linear, whereas that of the stele diameter to be exponential (Fig. 4). 4. The number of cortical layers, primary phloem poles (or vascular bundles) and the metaxylem vessels were considerably stable, while the thickness of the cortex parenchyma, stele diameter and root diameter were remarkably variable (Table 1). 5. Variation of the root diameter was attributable chiefly to that of the cortex parenchyma. The stele diameter was not responsible to the average radial length but to the number of component cells, whereas the thickness of the cortex to both characters (Fig. 5). 6. As it was observed that the primordia of the lateral roots initiated at the pericyclic portions opposite to the phloem strand, the increase in the number of phloem poles (or that of root diameter) suggested the potentiality for increase in the number of lateral rots.