Some eco-physiological aspects of seed dormancy in Geranium carolinianum L. from central tennessee.

In central Tennessee Geranium carolinianum L. behaves as a winter annual. Seed germination occurs in autumn, and seed ripening and dispersal are completed in May. Freshly-matured seeds have hard coats and will not imbibe water unless scarified. Embryos of freshly-matured seeds are conditionally dormant; scarified seeds germinate better in darkness than in light at high temperatures. After a short after-ripening period the embryo is essentially nondormant, and scarified seeds germinate to high percentages over a wide range of temperatures in both light and darkness. About 50% of the nonscarified seeds become germinable after 4.5 months of dry-laboratory storage. In order for the seed coat to become permeable (without scarification), seeds must be kept either dry or alternately wet and dry at relatively high temperatures during the summer dormancy period. The ecological significance of seed dormancy in G. carolinianum in central Tennessee is that it allows this non-drought tolerant species to avoid droughts that frequently occur in its habitat between late spring and early autumn. Conditional dormancy of the embryo of freshly-matured seeds, hard seed coats and the inability of seeds (non-scarified but permeable) to germinate in summer at high summer temperatures all seem to play a role in delaying germination until autumn.