FLOWER INDUCTION AND INITIATION IN CELERIAC (APIUM-GRAVEOLENS L VAR RAPACEUM (MILL) DC) - EFFECTS OF TEMPERATURE AND PLANT-AGE

Flower induction in (Apium graveolens L. var. rapaceum (Mill.) DC.) pl ants was studied by transferring plants from a low (12-degrees-C) to a high (20-degrees-C) temperature and vice versa at regular time interv als after sowing. There were 52 and 40 leaves, respectively, initiated on the apex of the main stem, prior to the initiation of the umbel (f inal number of leaves), of plants grown continuously from sowing at 20 -degrees-C and 12-degrees-C. Temperature during induction determined t his final number of leaves. Transfer of plants at different times duri ng the induction process resulted in a final number of leaves between 40 and 52. The degree of induction increased linearly with time of exp osure to inductive conditions, after the end of a short juvenile phase lasting until four to five leaves have been initiated on the apex. As soon as the induction was completed the final number of leaves was fi xed. Completion of induction and time of initiation of the inflorescen ce need to be regarded separately, because completion of induction was reached at a much lower number of initiated leaves than the final num ber of leaves. A temperature-determined final number of leaves and a v ariable time lapse between completion of induction and initiation of t he inflorescence on the apex prevents initiation of the inflorescence in young plants at a low number of leaves.