On the inhibition of bud development and other functions of growth substance in vicia faba

Abstract

Placing of terminal buds of Vicia faba on agar and subsequently assaying the agar on Avena showed that the terminal buds produce large amounts of growth hormone, and it seemed possible that it is this substance which causes the inhibition of lateral buds. Lateral buds, while undeveloped, were found to produce no hormone, but as soon as growth began (due to decapitation) hormone production became considerable. Parallel with this, the developing lateral buds have a marked inhibiting effect on other buds. Further, leaves, which have a slight inhibiting effect, were found to produce smaller amounts of growth hormone the amount decreasing with the age of the leaf. The proof consisted in applying purified growth hormone, in agar, continuously to the cut surface of the stem after removal of the terminal bud; if the concentration of hormone was sufficient then inhibition of laterals was complete; smaller concentrations produced partial inhibition. Since the growth hormone also promotes stem elongation in Vicia it thus has a double function, for which a theoretical basis is proposed. Other experiments showed that the hormone production takes place only in the light, but the response of the plant to a given amount of hormone, measured by growth, is greater in dark than in light. That the growth-promoting substance itself should inhibit bud development agrees satisfactorily with the observations recorded in the literature.