APPLICATION OF A THERMAL GRADIENT BAR TO STUDY OF GERMINATION PATTERNS IN SUCCESSIONAL HERBS

A thermal gradient bar was used to investigate the germination temperature optima (GTO) for various successional herbs. Four species of Plantago were investigated P. major and P. rugelii had a GTO of about 28 C, whereas P. aristata and P. virginica showed a GTO of about 16 C. These optima were correlated with germination patterns in the field. The first pair normally germinates in early summer at relatively high mean surface soil temperatures; the second pair germinates in fall at low mean surface soil temperatures. The thermal gradient bar appears to be a useful tool in dealing with these relations of phenology and physiology.