A Germination Inhibitor in the Seed Coats of Certain Varieties of Cabbage.

Freshly harvested seed of #1339-1-5, a selection miiade by the late C. H. MYERS, from Wisconsin Hollander, and various strains of Glory cabbage exhibit a pronounced dormancy and uneven germination, thus extending the breeding cycle from 1 to 2 years. This type of dormancy gradually disappears during several weeks of air-dry storage at room temperature, but by this time it is too late for field planting of seed produced in the greenhouse. We have been unable to find references in the literature to any type of seed dormancy in Brassica oleracea, but various types of more or less temporary dormancy in other species of Brassica seed have been reported from time to time. KIDD and WEST (1) were able to induce secondary dormancy in the seed of Brassica alba by low partial pressures of carbon dioxide. Later KIDD and WEST (2) found that the seed coats of Brassica alba restricted the gas exchange of the embryo during the early stages of seed maturity, but following maturity the seed coats gradually lost their ability to restrict gas exchange, along with the loss of vital activity of their cells. TAKIGUTI (5) reported that immature rape seed (Brassica napella) germinated readily, but when the embryo reached full development, germination of both intact seed and excised embryos dropped significantly. By the time the seed coat had completely matured the temporary dormancy of the embryo had disappeared, but the seed coats still restricted germination. TOOLE and TOOLE (6) tested samples of seed of Brassica alba, B. juncea, and B. campestris for germination at various lengths of time following harvest and found that the rate of germination increased with the length of the storage period. A growth-inhibiting substance in new crop mustard seeds has been reported by SHUCK (4).