VESSEL-DIAMETER DISTRIBUTION IN ROOTS OF GRAPEVINES (VITIS-VINIFERA LCV SHIRAZ)

The distribution frequency patterns of diameter of xylem vessels and p ercentage of total predicted axial conductances were studied in 190-da y and 212-day-old main roots of grapevines (Vitis vinifera L. cv. Shir az) grown under well-watered and stressed conditions. The protoxylem w ere the first to mature and were responsible for most of the theoretic al conductance in root segments between the tip and 2.5 cm from the ti p. Some large xylem vessels retained cross walls and protoplasm up to 22.5 cm from the tip. Statistical tests using the Kolmogorov-Smirnov t wo sample test showed that the pattern of distribution frequency of xy lem vessels classified in different diameter classes varied with dista nce from the root tip. The distribution frequency of xylem vessels was similar in both well-watered and stressed plants from the tip up to 1 5 cm from the tip. At distances further from the tip the distribution frequency of xylem vessels of well-watered plants was significantly di fferent from that of stressed plants, with the former having more larg er vessels than the latter. The pattern of vessel distribution frequen cy was different from that of percent total axial conductance (K(h)) p redicted with fewer large vessels carrying most of the axial flow.