The germination of seeds of Bidens pilosa L. colected at different pla
ces was analyzed by dose-response curves for induction and reversion o
f germination in seeds pre-incubated at 25 degrees C or 36 degrees C d
uring 24 hours. Our results indicate that phytochrome is responsible f
or the control of seed germination id Bidens pilosa and the level of p
re-existing active form of phytochrome (Pfr) above the threshold switc
h the seed to germinate in darkness.