Photoperiodic and thermal requirements for the flowering of Bryo phyllum daigremontianum (Hamet. et Perr.) Berg. and Bryophyllum tubiflorum Harv.
Marked differences were found between the photoperiodic responses of <em>Bryophyllum daigremontianum</em> and <em>Bryophyllum tubiflorum</em>, both species being classified as long-short-day plants (LSDP). The flowering of <em>B. daigremontianum</em> was observed under several photoperiodic conditions, among others under continuous exposure to long day (LD) or after transferring plants from a short-day (SD) to a long-day exposure: both conditions were regarded previously as non-inductive. It is argued that the flowering of <em>B. daigremontianum</em> is conditioned by sufficiently long LD exposure followed by one of two factors: the shortening of the day or the lowering of the temperature. The flowering of <em>B. tubiflorum</em> was observed only under more specific photoperiadic conditions, it seems to be conditioned by several successive changes of the length of the photoperiod.