IN his review of 1965, Paleg1 outlined the many biological tests that have been used as quantitative assays for gibberellins. The lettuce hypocotyl test is perhaps the simplest to carry out, but the lowest concentration that can be reliably assayed is only 0.1 mg/1. The most sensitive assay is the barley endosperm test which detects concentrations as low as 0.0001 mg/1., but this method has the disadvantage that the procedure is both involved and laborious.