STUDIES ON THE FORMATION AND SPROUTING OF AERIAL TUBERS IN BEGONIA EVANSIANA ANDR. X. TUBERIZATION UNDER LONG-DAYS AND IN DARKNESS

Abstract

1. Aerial tuber formation of Begonia evansiana Andr. known to take place usually in response to short-day conditions occurred also under long-day conditions, provided a part of the photoperiods was maintained at a lower temperature (chillng). Such a change of the critical daylength was marked in degree when the chilling temperature was from 9° to 13°. The effectiveness of the chilling was more pronounced when it was given during the later part of photoperiods, namely, just before nyctoperiods, than when given during the early part. No promotion of the chilling effect by sugar application was found. 2. If the plant was previously subjected to chilling under illumination, aerial tuber formation occurred in continuous darkness. The magnitude of this dark tuberization increased with decreasing the temperature and with prolonging the duration of the chilling. 3. If the plant was previously exposed to chilling, aerial tuber formation occurred in response to a single photoperiodic cycle, whose critical dark length was shorter than that in the standard condition. The magnitude of the tuberization was increased with the prolongation of the chilling period. The effectiveness of this previous chilling survived over one day even under illumination and a temperature of 30°. In a plant unexposed to the chilling, tuber formation required at least two cycles of short-days. 4. The aged plant which is known to tuberize in darkness was unable to respond to a single short-day. 5. Upon a modification of Gregory's scheme of the process of short-day response, the above findings were inclusively explained.