Germination ecophysiology of the woodland herb Osmorhiza longistylis ( Umbelliferae).

In N-central Kentucky seeds ripen in early to mid July, and dispersal begins in September and October. Although most of the seeds are shed during late autumn and winter, some remain on the dead shoots for up to 18 months. Seeds are dormant at maturity due to an underdeveloped embryo. Embryos grew at low (5oC) temperatures, but only after seeds were given a period of warm (30/15oC) stratification. With an increase in the length of the warm treatment, there was an increase in the number of embryos that grew to full length during a 12wk period at 5oC and an increase in the percentage of seeds that germinated. Seeds given 12wk of warm stratification required >8wk at 5oC to overcome dormany. Regardless of age and dispersal time, imbibed seeds must be exposed to high (summer or autumn) and then to low (winter) temperatures before they will germinate. Germination thus occurs only in spring.-from Author