Abstract
1. Some studies on the frost resistance of buds and twigs of apple trees were carried out.
2. One year-twigs of two varieties, Jonathan and Rails Janet, from 30-year old trees were used as material.
3. In cortical cells, the highest value of critical concentration of plasmolysis, 2.4_??_2.5M (glucose), was attained in December. This continued till the end of February and gradually decreased after the beginning of March.
4. The buds on twigs cut in January and February were not killed by exposure to temperature -20°_??_-25°C for a week.
5. It was found in buds on twigs cut in February that the longer the time of freezing, the lower the percentage of germination. Only 20% of total number of treated buds could be germinated after an exposure at -25°C for a week.
6. On the twigs in which cortical cells survived after a freezing, not all the buds always germinated.
7. In cortical cells of winter twigs, the longer the time taken for dehardening, the lower the cell permeability to water. The deplasmolysis time of cells dehardened for six days was five times that of hardy cells.
8. In the process of the freezing of living. cells, intra-cellular freezing as well as extra-cellular freezing was observed. In the latter case, none of the cells were usually killed by freezing. Intra-cellular freezing was, however, fatal without exception.
9. The mechanism of “splitting injury” of trunk by frost was briefly discussed.
