CHANGE IN DORMANCY STATUS OF FRASERA CAROLINIENSIS SEEDS DURING OVERWINTERING ON PARENT PLANT

Seeds of the monocarpic perennial Frasera caroliniensis ripen in late summer, and most of them are dispersed in late autumn and winter. However, some viable seeds may remain undispersed for more than a year. Embryos are underdeveloped (ca. 1.1-1.3 mm long) at seed maturity and do not grow while seeds remain on plants in the field. Dormancy in freshlymatured seeds was broken by 12 to 14 weeks of cold stratification at 5 C, during which the embryos elongated. On the other hand, seeds collected in January and March required a period of warm stratification followed by a period of cold stratification to germinate. Seeds collected in September and sown in a nonheated greenhouse germinated to 83% the first spring after maturation, whereas those collected and sown in January and March did not germinate until the second spring. Thus, seeds that remained on plants in the field until winter entered a deepened state of dormancy, and a warm (summer) followed by a cold (winter) stratification period was required to overcome it.