Influence of After-ripening on Phytochrome Control of Seed Germination in Two Varieties of Lettuce (Lactuca sativa L.)

The reversible photoreaction on seed germination of two varieties of lettuce differs remarkably not only with the variety but also with the germination temperature and the physiological conditions of seeds caused by after-ripening.Grand Rapids showed reversible photoreaction at 25 C with 0 to 6 months and at 30 C with 5 to 6 months after-ripening. MSU 16 did not show any reversible photoreaction at 30 C with 0 to 6 months or at 25 C with 0 to 3 months after-ripening although they were completely reversible with 4 to 6 months after-ripening.These two varieties of lettuce seeds, however, showed reversible photoreaction at 20 C when they were sown immediately after harvest or after 1 and 2 months after-ripening. The photoreversion decreased after the 4-to 6-month stage.