Wheat, pea and dwarf bean seedlings grown under controlled environmental conditions were used to assess the growth‐retardant activity of members of series of chloro‐substituted benzyl‐, trimethyl‐ and tri‐n‐butyl‐ ammonium bromides. The influence on activity of trialkyl groupings other than tri‐methyl and tri‐n‐butyl was also studied using compounds with the 4‐chloro‐benzyl ring structure. 3‐Chloro‐ and 4‐chloro‐benzyltributylammonium bromides were the most effective compounds. The activity was similar to that of 2,4‐dichlorobenzyltributylphosphonium bromide (Phosphon‐D) and they showed little phytotoxicity. A series of chlorophenoxymethyltributylammo‐nium and phosphonium salts were found to have lower activity than the corresponding chlorobenzyl derivatives. Allyldimethylsulphonium bromide retarded the growth of wheat seedlings but, like the aliphatic trimethylam‐monium bromides tested, it was only slightly active in the pea‐seedling test. The results are considered in relation to the chemical structure of the compounds studied. In particular, the influence of chlorine substitution in the ring of benzyltributylammonium salts on their growth‐retardant activity is compared with the effect of similar substitution on the auxin activity of phenoxyacetic acids. Copyright © 1969, Wiley Blackwell. All rights reserved
