1959 Volume 28 Issue 4 Pages 310-316
1. With the deceleration of the process of grow-th, the cane of rose becomes frost-hardy to some degree without being subjected to low temperature and then can be hardened further when they are subjected to low temperature. On the other hand, the growing cane is neither frost-hardy nor able to increase its frost-hardiness, even if it is subjected for ten days to 0°C. It is, therefore, very likely that in canes of the rose, the frost-hardiness as well as the abilty to be effectively hardened by ar-tificial chilling is closely associated with their stage of development. A variety that increase earlier its frost-hardiness in early fall has greater winter frost-hardiness than others.
2. The minimum temperature at which the canes of rose varieties are able to survive after 24 hours of freezing in winter are as follows: R. laevigata: -10°_??_-12°C, H. T., Floribunda, R. kordesii: -14°_??_16°C, H. P., Sub. Zero: -17_??_-18°C, Dorothy Perkins (Rambler): -20°C, R. multiflora, R. wichuraiana, R. setigera: -22°_??_-24°C and R. rugosa, R. pendulina: -27°_??_-28°C (Table 1).
3. In both natural and artificial frost-hardening of the parenchyma cells in the cortex of the rose, the increase in frost-hardiness of parenchyma cells is intimately proportional to that in their osmotic concentration (Table 2, Fig.2).
4. The canes of R. pendulina, and R. rugosa were immersed in liquid oxygen for 24 hours after pre-freezing for 16 hours at -30°C in order to draw from the cell interior almost all of the easily freez-able water by sufficient extracellular freezing. After having been thawed, they were planted in moist sand to test the capacity for development in green-house. The canes so treated put forth buds (Fig. 3); the parenchyma cells of their cortex were normally stained by neutral red solution and retain-ed their plasmolysis capacity (Fig. 4), but gradual-ly th canes withered because their inner cortex, pith-ray and pith periclinal tissue are less resistant to pre-freezing at -30°C than the parenchyma cells of cortex and buds.