XVI International Botanical Congess

Temperature requirements for embryo growth, dormancy-break and germination were determined for seeds of the North American species Sambucus canadensis and S. pubens, and of the European species S. racemosa. All three species have linear embryos that are about 70% fully developed at seed maturity. Embryos in freshly matured seeds of S. canadensis and S. pubens grew more at 25/15 than at 5oC. However, the rate of embryo growth in S. racemosa was greater at 5 than 25/15oC. Fresh seeds of all three species did not germinate during 2 wk of incubation. Cold stratification at 5oC for 12 wk broke dormancy in S. racemosa whereas none of those given 12 wk warm stratification germinated. Warm followed by cold stratification was effective to break dormancy of S. canadensis and S. pubens. Gibberellic acid was only partially effective in overcoming dormancy for S. canadensis and S. pubens but effective for S. racemosa