The progression of cavitation in earlywood vessels of Fraxinus mandshuricavar japonica during freezing and thawing

For an examination of the progression of cavitation in large-diameter early wood vessels of a deciduous ring-porous tree, potted saplings of Fraxinus m andshurica var japonica Maxim. were frozen and then thawed. The changes in the amount and distribution of water in the lumina of the current year's ea rlywood vessels during the course of the freezing and thawing were visualiz ed by cryoscanning electron microscopy. When samples were frozen, most of t he current year's earlywood vessels were filled with water. After the subse quent thawing, the percentage of cavitated current-year earlywood vessels g radually increased with time. All of the current year's earlywood vessels w ere cavitated within 24 h, and only limited amounts of water remained in th e lumina of earlywood vessels. Similar cavitation of earlywood vessels was observed after thawing of frozen, excised stem pieces. In contrast, many ve ssels of the current year's latewood retained water in the lumina during fr eezing and thawing. These observations indicate that the cavitation of the current year's earlywood vessels is not produced during freezing but progre sses during rewarming after freezing in F. mandshurica var japonica.