Determinants of germination success were investigated for cohorts of seed from Xanthorrhoea johnsonii A.T.Lee (Xanthorrhoeaceae) plants at four sites in Toohey Forest, Queensland Australia. Seeds were collected from individual plants for which plant height, date of first flowering had been determined. Germination success differed significantly among populations as a result of differential germination success, and among individual maternal plants. For example, all 10 maternal plants at the Griffith Road site had germination in excess of 80% while at the Forest Study Area germination of seeds from the 10 plants ranged from 20 to 100%. In a multiple logistic regression, this variation in germination performance was explained by both the time of first flowering and seed mass, but not by plant size: heavier seeds and those from early flowering plants had a higher probability of germinating. Germination probability was also significantly lower for seeds from the top third of the infructescence than from either of the other two thirds. These results suggest that germination probability in this species is influenced by both developmental conditions on the maternal plant and seed mass.