EFFECTS OF LEAF EXCISION ON FLOWERING OF XANTHIUM APICAL BUDS IN CULTURE UNDER INDUCTIVE AND NONINDUCTIVE PHOTOPERIODS

Apical buds of Xanthium were grown in aseptic culture under short-day cycles known to induce flowering in the intact plants or under “light-break” conditions known to prevent flowering. The total light provided in each 24-hr cycle was the same under the two photoperiods. Various numbers of leaves were excised from the apical buds. Excision of leaves did not change the response to photoperiod: even with all leaves excised the apical buds cultured under short-day conditions reached the same average floral stage as the control buds, and those under light-break conditions all remained vegetative. Fresh weight was not significantly changed by the excisions, either. However, excision of the young leaves resulted in an increase in the number of new leaves developed by the apical bud during the two-week culture period.