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Plant-derived smoke and aqueous extracts of smoke stimulate germination of dormant seed of the important fire-climax grass Themeda triandra (redgrass). The positive germination response to smoke increased as the state of seed imbibition increased. Furthermore, aqueous smoke extracts significantly increased seed germination at optimum and sub-optimum germination temperatures. Ethrel and ethylene, at a wide range of concentrations, failed to increase T. triandra seed germination, indicating that ethylene is not the active component of plant-derived smoke. Similarly, ash or aqueous ash extracts failed to stimulate germination. In contrast, aqueous smoke extracts prepared from burning fynbos vegetation and grass leaf material stimulated T. triandra seed germination. The bioactive component of plant-derived smoke may originate from a commonly occurring source, possibly being a thermal breakdown product of hemicellulose or cellulose.