Photoperiodic sensitivity of the cotyledon and first true leaf ofXanthium1

摘要

Three days after germination ofXanthiumseeds, the seedlings with only the first pair of opposite leaves attained full photoperiodic sensitivity and flowered in response to a 16-hr dark period treatment. The cotyledons of three- to six-day-old seedlings were completely insensitive to inductive dark treatment. Six-day-old seedlings could not be induced to flower with a 9-hr dark period. But with a dark period of 10 hr or longer, floral induction occurred and the optimum dark period was 15 hr. Development of the flowering apices started within 2 days after the inductive dark treatment and was completed by 9 to 11 days.