1)The photoperiodic sensitivity of Pharbitis nil can be evaluated by the minimum number of short day cycles and minimum duration of the dark period required for flower initiation, and by the readiness to initiate a terminal flower bud. The sensitivity of six strains tested stands in the following order: Tendan>Violet>Shifukurin>Nepal>Africa. Kidachi, a dwarf mutant, is an exception. It has the shortest critical dark period but seldom produces a terminal flower bud.
2) Grafting experiments indicated that the sensitive strain produces in leaves larger amounts of flowering hormone during a definite dark period, and is induced more easily to flowering in response to the same amount of floral stimulus than a less sensitive strain.