Unchilled seeds of Stachys alpina L. were dormant when harvested but germinated well if incubated in gibberellin. Chilling resulted only in limited increases in germination even after periods as long as 140 days. Endogenous gibberellins were not detectable in unchilled seeds, but extracts showed appreciable inhibitory activity. Chilling of the seeds resulted in increases in endogenous gibberellin-like substances and decreases in endogenous inhibitors. Significant levels of gibberellins were first detected after 50 days and continued to increase thereafter, while inhibitory activity was considerably reduced after periods exceeding 26 days.
The comparatively slow changes in endogenous gibberellin levels are discussed in terms of the limited germination response of the seeds to prolonged chilling.