SUMMARYXanthoria polycarpadischarged ascospores in the fall, winter, and spring. Discharge in the summer was infrequent. Spore discharge was correlated with rainfall. In the laboratory ascospores were discharged from 1 to 24 mm away from apothecia, and commonly occurred in groups of eight. Spore discharge occurred at 5, 10, 15, and 20 C. No discharge occurred at 25 or 30 C. Spores were discharged when apothecia were placed on moist filter paper or in an atmosphere of 100% RH. No discharge occurred at relative humidities less than 100%. More than 90% of ascospores incubated on water agar at 15 C germinated within 3 da. The highest percentage of spores germinated on plates incubated at 10, 15, and 20 C. Germination also occurred at 5 and 25 C, but not at 30 C. Spore germination was optimum atpH 5, 6, and 7. Spore germination on water agar and on lichen-extract agar was greater than germination on malt-yeast-extract agar or bark-extract agar.