抄録
Dormant one-year-old twigs collected from mature trees growing under different climates during mid-winter were artificially hardened at sub-freezing temperatures to overcome the differences of the sites of collection and to induce maximum freezing resistance. Evergreen broad leaf trees which range from the tropics in East Asia to the warm Pacific sea coasts can survive freezing to-5--7℃. Hardy evergreen broad-leaf trees and less hardy deciduous trees which have their northern limits of natural ranges in the northern Kanto District resistered freezing from -10 to -15℃. In these trees, the winter minimal temperatures appear to be the principal factor limiting the northern limits of their natural ranges. Most of the hardy deciduous trees which have their northern limits of natural ranges in northern Honshu and southern Hokkaido resisted freezing to only about -30℃. In these genera, the winter minimal temperatures appear to be the principal factor governing their geographical distribution in severe cold climates. In most of the more widely distributed deciduous species which extend to inland Hokkaido, Sakhalin and East Manchuria, the buds and cortical tissues of the twigs resisted freezing to -70℃.
