Spraying Experiments Against Apple and Pear Scab at Long Ashton and in the West Midlands,Season 1951

Ether extracts were made of samples of black currant berries (var. Seabrook’s Black) collected at weekly intervals from 18 days prior to fertilization until maturity. The extracts were shown to contain two acid auxins (a₁ and a₂), one neutral auxin (a₃), and one acid growth inhibitor (l₁), which could be separated by paper chromatography and assayed in biological tests. The changes in concentration of the three auxins throughout the season were studied in relation to seed and fruit development, fruit growth and fruit drop (“ running off ” and pre-harvest drop). It is suggested that the auxins are produced as by-products of either protein synthesis or hydrolysis taking place in different tissues and organs in a pre-determined order during the growth of the fruit. The rate of fruit growth showed a positive correlation with the concentrations of auxins I and 3, whereas fruit drop was negatively correlated with the concentration of auxin 2.