Abstract
The effects of coumarins on the germination and growth of white clover, red clover, timothy and orchardgrass were examined in this study. Coumarin at 10^<-3>M inhibited considerably the germination of white clover, timothy and orchardgrass, but not red clover. 4-Hydroxycoumarin, 7-hydroxycoumarin and trans-o-coumaric acid inhibited to a great extent the germination of timothy, but the other three species were comparatively resistant against these coumarin analogs. The germination of white clover, timothy and orchardgrass was inhibited even by coumarin at 10^<-4>M and that of orchardgrass was slightly promoted by coumarin at 10^<-6>M. The elongation of white clover hypocotyl and orchardgrass coleoptile was inhibited with increasing coumarin concentrations. This was also true for red clover and timothy at higher concentrations of coumarin. The elongation of red clover hypocotyl and timothy coleoptile was promoted by coumarin at low concentrations. The thickening of white clover and red clover hypocotyls, and of timothy and orchardgrass coleoptiles in the transversal direction was evoked by coumarin treatment.
