Jun Ohtani and Saizo Fujikawa

The free water in the vessellumina in sapwood and heartwood of Ulmus davidiana var. japonica was visualised using a cryoSEM technique, and related to the occurrence and morphology of tyloses. In the sapwood, ice crystals were present in a few latewood vesse1s but no tyloses were found. In the intermediate wood, ice crystals only occurred in some latewood vessels and many of the tyloses appeared to be collapsed in both earlywood and latewood vessels. In the heartwood, tyloses embedded within ice crystals were often observed. These observations suggest that in this species tyloses are not an obstacle to the accumulation of sap in heartwood vessels of living trees.