Phytochrome controls achene germination in Bidens pilosa L. (Asteraceae) by very low fluence response

Achene without ornament of the tegument were light insensitive with germina tion under all tested light conditions. Achene with verrucose ornament of t he tegument presented low germination under darkness and high germination u nder light conditions. By pre-incubation at 36 degreesC for remotion of pre -existing Pfr and by comparison of results of counting of dark germinating achenes at the end of experiment and daily under dim green safe light (0.00 1 mu mol m(-2) s(-1) nm(-1)) we concluded that germination was controlled b y phytochrome through very low fluence response.