2 TYPES OF MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF 2 GENERA (OSMORHIZA AND ERYTHRONIUM) WITH AN ARCTO-TERTIARY DISTRIBUTION PATTERN

Temperature requirements for embryo growth and germination were determ ined for seeds of Osmorhiza occidentalis, O. chilensis, and Erythroniu m grandiflorum collected in western North America (Utah). Initially, e mbryos were 1.2, 0.6, and 0.8 mm in length, respectively, and they gre w to 9.4, 9.2, and 4.1 mm, respectively, before germination occurred. Embryo growth and germination occurred during cold stratification (1, 5, 5/1 C), without a warm stratification pretreatment. However, warm s tratification pretreatments at 30/15 C increased rates of embryo growt h in O. occidentalis and E. grandiflorum seeds moved to low temperatur es and germination rates in all three species. Optimum germination tem peratures were 1, 5, or 5/1 C; gibberellic acid did not substitute for cold stratification. Thus, seeds of the three species have deep compl ex morphophysiological dormancy (MPD). In comparison, two species each of Osmorhiza and Elythronium from eastern North America have nondeep complex MPD and require warm followed by cold stratification for germi nation. Thus, disjunct species in genera with an Arcto-Tertiary distri bution pattern can have different types of MPD. It is suggested that d eep complex may have been derived from nondeep complex MPD.