ANNUAL CHANGES IN DORMANCY AND GERMINATION IN SEEDS OF SISYMBRIUM-OFFICINALE (L) SCOP

The effect of environmental conditions on changes in dormancy and germ ination of seeds of Sisymbrium officinale (L.) Scop. was studied. Seed s were buried in soil in the field or in incubators and at regular int ervals, germination of exhumed seeds was tested over a range of condit ions. Seeds that were buried in the field showed clear seasonal change s in dormancy. Fluctuations in soil moisture and nitrate content were not required for the changes in dormancy. Temperature seemed to be the only factor regulating these changes. Dormancy was relieved in period s of low temperatures and induced in periods of high temperatures. Fre sh seeds and seeds buried for only a few months germinated best at ele vated temperatures whereas seeds buried for a longer time germinated b est at low temperatures. Light, nitrate and desiccation stimulated ger mination of exhumed seeds. As a consequence, these treatments extended germination over a much longer period of the year. Germination of exh umed seeds in Petri dishes at field temperature was reasonably describ ed by a model based on the dual role of temperature, in the regulation of both dormancy and subsequent germination.