Studies on the Growth Hormone of Plants

Abstract

To determine whether a substance of the same genera] nature as the growth-promoting substance of Avena coleoptiles is responsible for the inhibition, by a terminal (or distal lateral) bud, of the growth of lateral buds below it, agar blocks of medium on which Rhizopus suinus had grown (i.e., containing "growth substance"), having an activity of about 2.10-6 mgm. per plant unit, and agar blocks into which "growth substance" which had diffused from decapltated terminal buds of Vicia faba, were applied to tops of decapltated plants; intact plants and decapltated plants to which plain agar blocks were applied being used as controls. "When the amt. of growth substance applied was of the same order as that diffusing from the terminal bud into agar (160 plant units every 6 hours), a slight but definite inhibition of the development of the lateral buds was observed. When, however, the amt. of growth substance applied was larger than that diffusing from the terminal bud (1400-1700 plant units every 6 hrs), the development of lateral buds was completely inhibited.".