Germination ecology of Bidens laevis (Asteraceae) from a tidal freshwater wetland1

LECK, M. A. (Department of Biology, Rider College, Lawrenceville, NJ 08648-3599), C. C. BASKIN AND J. M. BAsKiN (School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225). Germination ecology of Bidens laevis (Asteraceae) from a tidal freshwater wetland. Bull. Torrey Bot. Club 121: 230-239. 1994.-Eight or more weeks of cold stratification (5?C) were required to break dormancy in achenes of Bidens laevis (L.) BSP from a tidal freshwater wetland. When achenes began to come out of dormancy, they germinated to 50% first at 35/20?C, and then with additional stratification the minimum temperature for 50% germination decreased to 1 5/6?C. Germination of stratified achenes was inhibited by darkness and was completely prevented by hypoxia (inundation in closedjars). Seeds inundated in openjars and those in Petri dishes, however, germinated to > 80%. Germination declined sharply with depth of burial (0, 1, and 5 cm). Moisture regime (drained, saturated, and inundated) also significantly affected germination, but afterripening condition (cold greenhouse or 5?C) altered the effect. Interaction between depth of burial and moisture regime was significant (P 1 yr) following winter afterripening of achenes in the field.