Growth of stem internodes is promoted by another hormone, named gibberellin after the fungus Gibberella in which it was first discovered. The action of gibberellin on internode cells is also related to light intensity. In full sun the hormone’s effect on growth is somewhat restrained. Thus, while gibberellin promotes sufficient internode elongation to space the leaves, the structural stability of a squat growth form is maintained. In low light intensities, however, gibberellin becomes more active, causing internodes to stretch. By so doing the upper leaves are elevated to a position where they
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