Decapitation of tulips early in extension growth resulted in a 59% reduction in stem length at flowering. Selective removal of the floral parts showed that the gynoecium controlled stem extension. The upper internodes were most affected, and the effect was largely reversed by the application of indol-3-ylacetic acid (IAA) but not by gibberellic acid (GA). Soil drenches of ancymidol also reduced tulip stem extension, but in this case the lower internodes were most affected and this effect was reversed by GA.
The result of flower removal in narcissus was similar to that in tulip, although the narcissus scope and the tulip stem differ morphologically. Scape extension of narcissus was reduced by decapitation; this was due entirely to the removal of the gynoecium and could be reversed by IAA but not GA. In narcissus, spathe removal led to earlier flowering.
Flower blasting in tulip (a drying out of the flower which occurs commercially under some conditions) resulted from a number of treatments, including floral surgery, injections and ancymidol soil drenches. The incidence of flower blasting was reduced by injecting GA or kinetin.
The results are discussed in relation to commerical flower production, the control of pot-plant height, and the prevention of flower blasting.