When P. nil seedlings were exposed to a single inductive dark period, the main shoot apex and the lowest axillary bud which had not differentiated more than one leaf primordium underwent floral evocation within about 12 hr of the end of the dark period. The higher axillary buds appeared to be evoked in acropetal sequence over the following 2 days at 28�C, or 4 days at 21�C.