Abstract
It is known that the roots of rice plants branch out from the secondary to the sixth order lateral roots, and there are, generally, two kinds of lateral roots can be seen at any order, namely, thick and thin lateral roots. Their structures differ in that the thin lateral roots are absent in the late metaxylem elements (MX II) and in the cortex which forms lysigenous aerenchyma (Fig. 1, B and C). The vessel connection between the crown root and the secondary lateral root, between the secondary lateral root and the tertiary lateral root, and so on, are alike. In other words, the protoxylem elements (PX) of the lateral root are connected with the protoxylem elements or early metaxylem elements of the parent root, and the late metaxylem elements (MXII) of the lateral root are connected with the late metaxylem elements of the parent root, independently of the order (Figs. 3, 4 and 5). Between the vssels of the lateral root and the parent root, at the connecting region, tracheary elements (TE) were observed which may be modified forms of the stelar parenchyma cells, and these tracheary elements were jointed with the side wall with each other (Figs. 3, 4 and 5). The connection between the protoxylem elements (or the early metaxylem elements in the case of the crown roots) and the late metaxylem elements in the parent root was observed at the region where the lateral roots were formed. The connection might be undergone by modification into tracheary elements of the stelar parenchyma cells between them (Fig. 6). Some of these tracheary elements had perforations and others did not (Fig. 7).
