Morphogenetical studies on the stem pitting in citrus trees. III

Abstract

The rays in the xylem of citrus trees were classified into two types (Fig. 1 and 3). One was uniseriate and the number of cells in the height (the length of axial direction) of tangential section of the ray was usually 1 or 2 through successive stages of the secondary growth. Another was uniseriate in the earlier stage of annual ring development and underwent change to multiseriate in the later stage. Many papillae were found not only on surface of the walls of the ray cells, but also on surface of the walls of parenchymatous cells, fibers and pith cells (Fig. 9, 10 and 13). Such cells appeared to be interconnected with each other morphologically by the papillae. The number of papillae on the outer or inner tangential walls of such cells were more than those on the upper or lower transverse walls. From these results it may be estimated that ray cells have some physiological interconnection in radial direction of secondary wood by the papillae.As mentioned in the previous paper18), abnormal tissues associated with the stem pitting were formed in ray initials of the cambium instead of differentiation into normal multiseriate ray cells. Furthermore the abnormal tissues were found to be more remarkably in parenchymatous tissues than in fibrous tissues of the wood. From these results, it may be assumed that the formation of abnormal tissues is related with the differentiation of parenchymatous cells during the secondary growth. Concerning the general pattern of variation in annual wood ring, it was clarfied that during secondary growth the cambium produced almostly fibrous cells in summer season and differentiated parenchymatous cells in winter season.These facts and assumption suggest that the abnormal tissues and parenchymatous tissues are formed in the same season and may be influenced by physiological condition of the cambium. In other words, the stem pitting phenomenon on the wood of citrus trees might be depend on cambial condition in a given season of a year.