Higazy tried to determine whether the duration of the juvenile phase for flowering was a fixed character or whether it could be influenced by external growth factors.Lunaria biennis was chosen as a cold-requiring biennial, Silene armeria as a long-day plant and Salvia occidentalis as a short-day plant. In L. biennis photosynthesis shortened the juvenile phase. In general young plants could not be vernalized and especially in dim light remained completely juvenile. Older plants after either bright light or dim needed relatively little cold. There was an intermediate transitory stage, requiring more cold the younger the plants, especially after dim light. Incomplete vernalization resulted mainly in lateral flower buds, which was explained by leaf vernalization. Soil moisture, N, P and K hardly shortened the juvenile phase. Gibberellic acid (GA) lowered the percentage of generative plants in every age group for bright light after vernalization during 12 weeks, and hence tended to maintain juvenility. GA accelerated however the realization of flower bud formation after both bright or dim light.The short juvenile phase of S. armeria could be reduced by 18 to 27 days of bright light. GA reduced it only a little, especially with bright light. Salvia occidentalis tended to flower more if propagated vegetatively than from seed. Light intensity had no influence and GA only a slight influence.So factors promoting vegetative growth and prolonging active growth would shorten the juvenile phase of herbaceous plants.
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