Seed dormancy pattern of the annuals Argemone ochroleuca and A. mexicana (Papaveraceae).

Summary Seed dormancy of the tropical annual weeds Argemone ochroleuca Sweet and Argemone mexicana L. was studied in a series of experiments. Factors investigated included: light, darkness, five temperature regimes and combinations of periods of light, darkness and the different temperature regimes for various time periods (up to one year). Furthermore, germination in solutions of gibberellic acid, after leaching, after mechanical treatments, and after periods of dry storage, was studied. Since the seeds have underdeveloped embryos, their growth was also studied. There was no, or very little, germination ( Argemone ochroleuca after-ripened slightly and germinated to 10–20% after one year of dry storage. Germination to 100% occurred only after artificial treatments, either after removal of part of the seed coat and endosperm or after incubation in gibberellic acid solution. The significance of the strong dormancy was confirmed in the field for A. ochroleuca when only 8% of seeds sown produced seedlings in the first season after shedding. We conclude that the majority of seeds normally do not germinate during their first season after shedding, but instead enter into the seed bank, thus producing seedlings, even in a well-maintained field, probably for several years.