Photoperiodic Floral Induction of Xanthium and Germination of Lettuce Seeds Implanted in the Petioles

Abstract

1. The germination of lettuce seeds implanted in petioles of Xanthium plants under light-tight aluminum foil wrappers showed an inverse correlation with the duration of the photoperiod to which the host plants were exposed. 2. This lettuce-seed-germination response appeared to be directly related to the duration of light to which the Xanthium plants were exposed rather than to the total light energy they received. 3. The evidence thus far obtained strongly suggests that the germination response is correlated with metabolic changes associated with floral induction of the host Xanthium plants. 4. The germination response can be interpreted as an inhibition of germination of seeds implanted in petioles of Xanthium plants exposed to long-day conditions, although a stimulation of germination when the host plants are under short days has not been excluded. 5. The identity of the naturally occurring inhibitor is not known; the possibility of its being xanthinin, coumarin, or indoleacetic acid has been eliminated...