Penstemon palmeri is a short-lived perennial herb colonizing disturbed sites in semiarid habitats in the western USA. In this study seed was harvested from six native and four seeded populations during two consecutive years. In laboratory germination trials at constant 15 C, considerable between-lot variation in primary dormancy and light requirement was observed. Four weeks of moist chilling (1 C) induced secondary dormancy at 15 C. Cold-induced secondary dormancy was reversed by one week of dark incubation at 30 C. This warm incubation treatment also reduced the light requirement of unchilled, after-ripened seed. Fluctuations in dormancy and light requirement of buried seeds have been linked to seasonal changes in soil temperature. Penstemon palmeri germination responses to temperature appear to be similar to those of facultative winter annuals.
Kitchen, Stanley G. and Meyer, Susan E.
"Temperature-mediated changes in seed dormancy and light requirement for Penstemon palmeri (Scrophulariaceae),"
Great Basin Naturalist: Vol. 52
, Article 7.
Available at: http://scholarsarchive.byu.edu/gbn/vol52/iss1/7