Wet calendula seed was incubated at 45.C for 0, 2, 8, or 24 h followed by incubation at 16.C for a total cumulative incubation period of 24 h. Following modified procedures from the Tetrazolium Testing Handbook (Peters, 2000), seeds were bisected longitudinally, and the largest portion of the embryo was excised.There were 20 seeds per plate and 3 plates per treatment. The experiment was repeated twice. All 20 embryos from each plate were placed in 1 ml of 0.1% tetrazolium chloride solution and stored in the dark at room temperature for 4 h. Seeds were rinsed in 2 volumes of MiliQ water and scored for viability. Seeds only were considered viable if the entire embryo stained bright pink. All embryos with partial staining were recorded as dead. Percent viableseed was calculated for each treatment.