Abstract
This study was carried out to clarify the effect of low temperature on the bulb or corm formation of the seedlings in the eight kinds of ornamental plants which produce the bulbs or corms in early summer.
The results obtained were summarized as follows:
1. When the seedlings of Allium atropurpureum and A. neapolitanum were maintained at 20°C under long day-length conditions for approximately 140 days, their bulbs were not formed, however, when the seedlings of 4-5-foliage stage were exposed to 5°C for 30 days or 10°C for 50 days, they produced the normal bulbs under 20°C and long day-length.
2. From the results showed in Figs. 1 and 2, it is considered that the requirements of low temperature for the corm formation in Freesia hybrida and bulb formation in A. pulchellum were lower than that in A. atropurpureum and A. neapolitanum. When the germinated seeds of Freesia were exposed to 5°C for 73 days under wet conditions and thereafter they were grown at 20°C, the seedlings produced the corms rapidly.
On the contrary, the requirement of low temperature of A. porrum for the bulb formation was the highest among the tested materials, hence the seedlings of this species became gradually to respond to low temperature as it had grown to a certain size.
3. The seedlings of A. flavum, A. heldreichii and Babiana stricta did not form the bulbs under 20°Cconditions, but their bulbs or corms formation were accelerated after these seedlings were exposed to low temperature.
4. From the results obtained by this investigation, it is considered that the bulb formation in the bulbous plants occurred after they were exposed to low temperature during a certain duration.
Accordingly, it was sure that the bulb formation in the bulbous plants which produce the bulbs or corms in early summer is caused by the seasonal thermoperiodicity as if the flower formation were caused by the vernalization.
