The Effect of Indoleacetic Acid upon Initiation and Development of Hypocotyledonary Bud Primordia in Flax

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Abstract
1. The decapitated hypocotyl of flax, with its initial injury and the resultant injury effects, is in a pathic state during the course of the experiments reported here. The metabolic status of the hypocotyl at the moment of infliction of the injury, and the external conditions to which it is exposed after its mutilation, determine to what extent the injury effects terminate in recovery and shoot regeneration, or in death. 2. Single or repeated applications of lanolin alone to the wound of the decapitated flax hypocotyl produced no detectable effects upon survival of the hypocotyl or upon its initiation and development of hypocotyledonary buds. 3. Applications of 3% and of 1% indoleacetic acid in lanolin to the decapitation wound completely and permanently inhibited bud primordium development in the lower half, and bud primordium initiation in the upper half, of the hypocotyl. The treated plants died earlier than the untreated cut controls, as reported earlier for bean and tomato. 4. Application of 0.3% indoleacetic acid in lanolin retarded these bud events for a long time. It also led to the premature death of most of the treated hypocotyls. Application of 1:1 (0.116%) indoleacotic acid in lanolin led to slight retardation or to complete inhibition of these bud events, depending upon the number of treatments and upon the metabolic status of the tested plants. 5. The lowest concentration of indoleacetic acid noted to retard bud primordium initiation and development was 1:128 (0.0009%). One treatment with this concentration in February was more effective than repeated treatments in May. 6. While one treatment with 1:16 (0.007%) concentration of indoleacetic acid retarded grossly detectable bud appearance for 17 days, repeated treatment suppressed it completely for 26 days. 7. In the higher concentrations, 1:4 (0.029%) and above, no difference was noted in the effect of single as compared with repeated treatments. 8. Under the conditions of the experiment no concentration was found which stimulated bud primordium initiation and development. 9. The findings show that indoleacetic acid in lanolin may retard or completely inhibit the transverse divisions of epidermal cells of the hypocotyl which are the first detectable beginning of hypocotyledonary bud primordium initiation in flax. 10. The greater efficiency of repeated applications than of a single application of the same concentration of indoleacetic acid in inhibiting or retarding these events may indicate that the former treatment maintains the threshold necessary for inhibition by replacing auxin used up or bound in the hypocotyl.