Developmental Changes of Rays in Stems of Selected Woody Dicotyledons

抄録

This study was carried out to investigate the developmental changes and the origin of primary and secondary rays in relation to secondary growth of Robinia pseudoacacia, Albizzia julibrissin, Diospyros kaki and Castanea crenata. Primary rays were highly uniseriate and mainly of vertical elongated cells. They were the products of repeated divisions of short cells in the procambium. The first secondary rays arose in the fasciular region at a distance of 500-1000μ from the pith and originated by dividing off the sides or ends of fusiform initials. In R. pseudoacacia ray height increased in the late wood of the first growth ring, and then kept constant after a gradually decreasing in the second growth ring. While in A. julibrissin, D. kaki and C. crenata, ray height remained constant through the secondary growth after marked decrease in the first growth ring. Ray width gradually increased in all samples, however, the number of rays per unit area decreased with exception of D. kaki. The ratio of rays to axial systems gradually increased in R. pseudoacacia, A. julibrissin, and D. kaki. But in C. crenata the height and ratio of rays remained constant throughout the secondary growth.