In eastern Washington Dalmatian toadflax (Linaria dalmatica(L.) Mill) produces seeds for about 3 months, beginning in early July, with over 95% produced during the first 5 weeks. A large plant will produce a half million seeds under good conditions. Seeds are sharply angular, slightly winged, and 1 to 2 mm long. Approximately 7,000 weigh 1 g. Seeds are spread by wind and browsing animals. Some seeds will germinate under laboratory conditions the same season in which produced, but germination from dry storage increases for 2 to 3 years, with a periodic low in November and a high in April. Over 90% germination is obtained with 2 to 3-year-old seeds in the laboratory. Germination in the field occurs in both spring and fall, and seedlings can emerge from a soil depth of 2 to 2.5 cm.
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The longevity of brown and black forms of seed of halogeton (Halogeton glomeratus (M. Bieb.) C. A. Mey.), buried at four depths, was determined for a 10-year period in Nevada, Idaho, Utah, and Washington. The black form of seed had almost 100% field germination at all depths by the end of the first year and had completely germinated or was nonviable by the end of the second. Brown seed on the soil surface began field germination the first year at all locations and had germinated or become nonviable at the end of 6 years. Burial at 1, 3, and 6 inches delayed the peak of viability and tended to increase longevity of brown seed. Germination was less than 0.5% at the end of 10 years, and viability was near zero under both field and laboratory conditions. Seed germinated and lost viability most rapidly in Washington, the location where most favorable winter conditions for germination occurred.
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