Changes in Apical Growth and Phyllotaxis on Flowering and Reversion in Impatiens balsamina L.

When plants of Impatiens balsamina L were subjected to 5 short days and then re-placed in long days, they began to form a terminal flower and then reverted to vegetative growth at this terminal shoot apex The onset of flowering was accompanied by an increase in the rate of initiation of primordia, an increase in the growth rate of the apex, a change in primordium arrangement from spiral to whorled or pseudo-whorled, a lack of internodes, and a reduction m the size at initiation of the primordia and also of the stem frusta which give rise to nodal and internodal tissues On reversion, parts intermediate between petals and leaves were formed, followed by leaves, although in reverted apices the size at initiation and the arrangement of primordia remained the same as in the floweing apex The apical growth rate and the rate of primordium initiation were less in the reverted apices than in floral apices but remained higher than in the original vegetative apex Since the changes in apical growth which occur on the transition to flowering are not reversed on reversion, the development of organs as leaves or petals is not directly related to the growth rate of the apex, or the arrangement, rate of initiation or size at initiation of primordia