Gibberellin controls seed germination, and ethylene promotes stem thickening, especially in seedlings. In some species at least, abscisic acid brings on dormancy, whereas gibberellin revives them from winter sleep. In some species, artificially applied gibberellin promotes flower formation and increases fruit size. Ethylene initiates flowers in pineapple and its relatives (the bromeliads), which, according to some reports, need only be enclosed in a bag with apple peelings for several days to produce flowers. Unfortunately, neither ethylene nor gibberellin is universally effective as a
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