Studies on elements of the wood in rice plants

Abstract

Various size and forms of vessel members, parenchyma cells, and fibers were found in roots, leaves and stems of rice plants. The primary walls of protoxylem vessels in leaves and stems were always found destroyed, so it was not made possible to observe their size. The metaxylem vessels of each organ were divided into two types according to length and diameter of their elements; some were longer having smaller diameters (metaxylem I) while others were shorter with larger diameters (metaxylem II). Out of all wood elements, fibers in each organ were the longest with smallest diameters sometimes having wave-like roughness on their surface. In the nodes of stems, various forms of metaxylem vessels with many perforations were found. By the observation on leaves it is assumed that the vessels of connecting tissues are composed of elements of metaxylem. In the protoxylem of each organ, two types of thickening were found, that is annular and spiral. In leaves and stems, especially the wall of annular elements thickens conspicuously. On the contrary, in roots, the thickening of both these two types of elements is less. In the metaxylem I, many types of thickening were observed. In leaves, annular and spiral elements are dominant. In roots and stems besides these, scalariform and pitted ones could also be observed. In the metaxylem II, the type of thickening of vessel elements differs in different organs. In leaves, a kind of scalariform elements is most common. In roots, on the contrary, the most common type of thickening found is pitted. In stems, the thickening shows the intermediate type between those found in roots and leaves. The parenchyma and fiber cells of xylem also show thickening in their cell walls. The walls of fibers are pitted with the pits distributed sparsely. On the walls of parenchyma cells, much variation in the type of thickening was observed. It sometimes resembles that of vessels and sometimes that of fibers. The perforation plate of metaxylem II can be divided into several types, that is, simple transverse, simple oblique, scalariform and tracheid-like. The former two are commonly found in rice plants. But in the shoot, especially in leaves, the latter types are frequenty observed. It is assumed from these observations that the roots are evolutionally the most advanced and the leaves the most primitive organs of the plant.