Factors Controlling Elongation of the Last Internode in Tulip Flower Stalk

Abstract

Elongation of the last internode of _??_ntact tulips was inhibited by dark or ancymidol treatment. More diffusible auxin was obtained from the last internode of light-than dark- or ancymidol-treated plants. GA₃ application recovered the ancymidol-mediated reduction in elongation and content of diffusible auxin. Decapitation reduced elongation of the last internode. IAA recovered the reduction in elongation, but GA₃ alone did not. The effect of IAA with ancymidol or with dark treatment on elongation of the last internode was less than that of IAA+GA₃. It is suggested that elongation of the last internode is controlled by auxin and gibberellin, as was previously shown with the first internode.