The Effects of Certain Growth-regulating Substances on the Rhizomes ofAegopodium podagraria

Abstract

1. The effects on elongation and geotropic behaviour of the immersion of rhizomes of Aegopodium podagraria for periods of minutes in solutions of β-indolylacetic acid,2:4-dichiorophenoxyacetic acid, ascorbic acid, 2:3:5 -triiodobenzoic acid, and 2:4-dichloranisole were investigated. 2. The experimental treatment was carried out in absence of visible light, the rhizomes being photographed every hour by infra-red radiation. 3. After immersion in 10 ⁻ M. IAA, the rate of growth is approximately doubled. About 5 hours later it declines to one-third or less of its original value and then gradually recovers. The depression in the growth rate can be reversed by a second immersion in IAA, indicating that it is not due to exhaustion of some other substance essential for growth. 4. Immersion in 10 ⁻⁴ M. 2:4-D also stimulates growth, which then slowly returns to about the normal rate without showing any marked depression. 5. The possibility is suggested that IAA, which first accelerates elongation, is later converted into, or causes the production of, an inhibitor. When successive immersions in IAA are repeated every 2 hours, the inhibition can be partially overcome so long as the treatment is continued. 6. Ascorbic acid slightly depresses the rate of elongation, but triiodobenzoic acid and dichloranisole produce no significant effect. 7. Immersion of the horizontal rhizomes in IAA or 2:4-D causes them to turn up. This suggests that an equilibrium is disturbed and supports the hypothesis that the diageotropic behaviour of these rhizomes is the result of a balance between the effects of two opposing hormones.