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Degree Name

Doctor of Philosophy




Environmental influences on the after-ripening and dormancy of seeds of a number of species were studied in the field and laboratory;Environmental dormancy is defined as the type of dormancy affecting a readily germinable seed when it was prevented from germinating by absence of some essential environmental factor or by the presence of some inhibitor, and seed dormancy, embracing both primary and secondary types, as the dormancy existing in a seed which fails to germinate under apparently satisfactory germinating conditions;The after-ripening of seeds of Thlaspi arvense, Brassica arvensis and Avena fatua was studied (1) in fine sandy loam, (2) in clay soil, (3) on the soil surface, and (4) in dry storage. Conditions for the fall after-ripening of Avena seeds were better on the ground surface or in dry storage than in the two soils; seeds of Thlaspi were favored by limited moisture in the fine sandy loam soil, and failed to after-ripen while on the ground surface; Brassica seeds failed to show significant after-ripening during the fall in any of the environments. Most primary dormancy, however, disappreared from the seeds of the three species during the winter and early spring. This type of dormancy is, therefore, probably of little significane in the longevity of seeds of these weeds;Although secondary dormancy was produced experimentally, none was found in any of the seeds of Thlaspi in the field, and only isolated instances of it were found in seeds of Brassica. Like primary dormancy, secondary dormancy appears to be of little importance in the longevity of seeds of these weeds in the soil;Seeds of Thlaspsi arvense and Brassica arvensis were generally found to be in environmental dormancy after lying several years in the soil. Our work indicates that inadequate aeration is the main factor preventing the germination of these seeds. Experiments in different gas concentrations showed that seeds of weeds and crops which germinate readily in the field were tolerant to adverse gaseous environments, while seeds which display pronounced environmental dormancy, like Brassica and Thlaspi, were very sensitive to low oxygen or to high carbon dioxide pressures. (Abstract shortened by UMI.)



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Robert Owen Bibbey



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168 pages