2.2. Gradient bar temperature incubations
Seeds were germinated on a temperature-gradient bar lined with filter paper as described by Berti and Johnson (2008) for 9 d with nine thermal couple probes evenly spread along the bar in the range of 1.1–39.0◦C. The thermocouples (copper-constantan)were attached flush to the aluminum bar with high temperature conductivity epoxy resin. The thermocouples were monitored with a CR-10X (Campbell Scientific, Logan, UT) data logger every 15 sand 1 h averages recorded. Seeds were placed in 3 rows of 10 at each thermal couple, each row served as an experimental replicate.Seeds were checked daily for germination and filter paper was re-moistened as needed. Radical emergence of greater than 0.5 cm was considered germination, and the germinated seed was removed from the gradient bar. The entire experiment was performed three times.