To obtain one of the physioecological characteristics of the vulnerable plant species Pulsatilla cernua, we determined the base temperature and thermal constant of the germination of this species. We examined the germination time courses at five constant temperatures (10, 15, 20, 25, and 30°C) and used them for the nonlinear fitting of an exponential distribution with a lag phase. The distribution showed excellent goodness of fit to the observed germination time course at any temperature. We linearly regressed germination rate, which is a reciprocal of the duration for 50% germination of P. cernua seeds, against temperature to calculate the base temperature and thermal constant of seed germination. The linear regression showed excellent goodness of fit. The calculated values were 6.57°Cfor the base temperature and 142 degree days for the thermal constant. Using the base temperature, the thermal constant, and the daily air temperatures at the study site, we can predict that the seedling emergence of P. cernua will occur in the summer season.
