A period of 1 to 3 days imbibition followed by drying altered the subsequent germination responses of seeds ofRumex crispusL. When the imbibition took place under alternating light and temperature conditions subsequent germination was faster and more complete. In contrast, when the seeds imbibed at a constant temperature and in nearly continuous darkness subsequent germination was delayed and less complete. Subsidiary tests demonstrated that (a) within a 24-h drying period, the seeds lost virtually all water imbibed over 1 to 3 days; (b) a 3-day imbibition pretreatment was followed by faster, more complete germination in a 0.25ensp;M mannitol solution; (c) the duration of the drying period (up to 29 days) had little effect on the outcome; and (d) seeds pretreated for 1 to 3 days under an alternating light and tempegrave;rature regime germinated more rapidly than untreated seeds when sown in soil in a greenhouse. These results help to explain why seedlings ofR. crispasappear rapidly each summer following a drought-ending downpour, whereas seeds of the same species buried deep in the soil acquire a secondary dormancy and may remain viable for up to 80 years.
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