Fully ripened oospores from two clones of Chara Zeylanica Klein ex Willdenow. were harvested in October. Initially, the oospores of one clone were all dormant, those of the second clone were non-dormant. Postharvest temperatures influenced after-ripening and dormancy initiation respectively. The temperature effect was reflected in the amplitude of germination, which ranged from 29-100% hut not in the duration of the dormant interval. The germination window opened independently of temperature and was maximally open 6-2 months postharvest. After-ripening was augmented and germination was suppressed by oscillating temperatures. Light, given as prolonged exposures, was a necessary stimulus for activation. A secondary, or ‘Haupt’, messenger, diffusing from the bactoagar substratum, obscured the light reaction and disrupted the germination window. A ‘location awareness’ is suggested by an endogenous temporal window of germinability, superimposed on which are discriminators that sense appropriate conditions of light and temperature.