The frost-hardiness of bulbs and tubers

Abstract

1. The frost-hardiness of bulbs and tubers varies according to their stages of development and internal conditions. The bulbs and tubers of tulip, lily, crocus, hyacinth, etc., become frost-hardy to some degree without being subjected to low temperature, when they mature sufficiently, and then they can be hardened further when they are subjected to low temperature. On the other hand, the bulbs and tubers of gladiolus, freesia and anemone are neither frost-hardy nor able to increase their frost-hardiness even if they would be subjected to 0°C. The ability to undergo effective hardening by artificial chilling is closely associated with the degree of their frost. hardiness (Table 2). 2. The minimum temperatures at which the bulbs and tubers are able to survive after 24 hours of freezing in winter are as follows: Lilium dauricum (Ezosukashi) Muscari (-15°_??_-18°C)>Ornithogalum (-12°_??_-13°C)>Narcissus poeticus (-10°_??_-12°C)>Tulip (var. Mozart) Crocus (var. Large Yellow) (-10°C)>Lilium speciosum (var. rubrum), Nar-cissus, Iris hollandica, Hyacinth, (var. King Alfred), Ixia (-7°_??_-8°C)>Montbretia Antholyza (-5°C)>Anemone, Gladiolus colvillei, Freesia (-3°_??_-4°C) 3. Dried tubers (water content below 25%) of anemone and ranunculus were immersed in liquid nitrogen (-196°C) for 24 hours. After having been warmed, they were planted in moist sand in green-house to test whether they were able to grow. The buds were put forth from the bulbs so treated and grew normally (Fig. 1). From this fact, it seemed that the easily freezable water in cells of these bulbs have been lost by desiccation, and that the bulbs in this state were not injured even when exposed to the extremely low temperature. On the other hand, when the bulbs had adsorbed water sufficiently, they were damaged by freezing even at -5°C. Accordingly, without intracellular freezing, the degree of cold does not seem to exert any important effect upon the bulb, and also it seems that the low temperature itself cannot be a primary factor of damage by freezing.