Abstract: This paper describes a new and convenientt rootformation test. It is excised cucumber cotyledon root-formation test. The experimental results showed that the mininum level of IAA detectable in this bioassay was 0.3–100 ppm and the number of roots formed in excised cucumber cotyledon was proportional to the logarithm of the IAA concentration in the range of 3.0–30 ppm. This bioassay is specific for natural and synthetic auxins. It had less error and better repeatability than others.

Key words: Excised cucumber cotyledon, Auxins, Root-formation test