Temperature and Imbibition Influence Seed Germination Behavior.

The direct role of physical dormancy in delaying germination of Bentham, Fosberg, and Merrill seeds has not been adequately studied, nor has the role of temperature on germination behaviors. Imbibition testing indicated seeds with scarified testa absorbed water for the duration of a 24 h imbibition period, but seeds with an intact testa stopped absorbing water after 1 h. The behavior of seeds most closely matched those of , with the pattern of water absorption for seeds deviating from that for the other species. Scarified seeds germinated readily, with initial germination occurring by 50 h for and 90 hr for the other species, and maximum germination of 80% to 90% occurring by 60 h for and 100 h for the other species. Predicted optimum temperature based on a fitted quadratic model was 26 °C for , 23 °C for , and 22 °C for . Seed respiration increased within 3 h of imbibition for scarified seeds and continued to increase in a linear pattern. The linear slope was greatest for , intermediate for , and least for , but ultimate respiration was greatest for seeds. Seed respiration was so limited for un-scarified seeds that the instrument was unable to quantify any carbon dioxide efflux. Physical dormancy in seeds of these Serianthes species is a powerful trait that spreads out the timing of seedling emergence in natural settings and controls imbibition and germination speed in managed nurseries.