THE IN VITRO SECRETION OF GROWTH REGULATORS BY ISOLATED

A B S T R A C T Tissues from a wide variety of plants were surface sterilized, isolated, and grown on different media. These isolated tissues were bioassayed for growth regulatory activity. The secretions from four of the 20 callus tissues inhibited the growth of Bacillus subtilis. An aseptic method for measuring the growth of Lemna was developed and used to detect inhibitory materials in medium which had supported the growth of five isolated callus tissues. In the seed (Lycopersicon esculentum) germination test five callus tissues had an inhibitory influence while two callus tissues showed a stimulatory effect. The study also included expressed juices and extracts of callus tissues which secreted regulatory materials. The expressed juice of five callus tissues contained materials which inhibited the growth of Lemna. Two expressed juices inhibited the growth of Bacillus subtilis. The water extract of two callus tissues inhibited the growth of Lemna. Fifty percent of the plants which have been reported to produce growth regulatory materials in nature also produced callus tissue which was capable of regulating growth of assay organisms. NATURAL GROWTH INHIBITORS and their important role in plant ecology and competition has been well documented in the plant kingdom. Cook (1921) and Massey (1925) investigated the response of plants growing in the immediate vicinity