The relationship between the constitution and the effect of chemical compounds on plant growth. IV.—derivatives and analogues of 2‐benzoylbenzoic acid

Selective inhibition of the root growth of germinating seeds is shown by compounds in which a benzene or naphthalene ring is linked in the ortho‐position to benzoic acid by CO, CH2, NH or CO‐NH. Rape is usually more susceptible than wheat. The effect of substitution in the benzene ring and of esterification has been examined. 2‐(4‐Phenyl‐benzoyl)benzoic acid and N‐α‐naphthylphthalamic acid were found to be the most active compounds. Some compounds of these classes abolish the normal geotropic responses of rape and rye‐grass roots at concentrations below those at which there is marked inhibition of root growth. High activity was found particularly in the benzoylbenzoic acid and phthalamic acid series. Examination of a few of the compounds reveals that they also affect the phototropic response of shoots of rape and rye‐grass.