Published online by Cambridge University Press: 11 June 2012
Floral ontogenesis has long been a preoccupation of morphologists. In trying to understand the physiological mechanism that underlies and determines the orderly formation of the several kinds of floral organs, it is essential to consider the organization and functional activities of the apex of the antecedent leafy shoot. The most general characteristic of the growing shoot apical meristem is that it gives rise to a succession of regularly spaced leaf primordia, sometimes of very variable form and structure, these having their inception in loci of special metabolism, or growth centres. The latter, typically originate in the sub-distal region of the meristem. The initial state of this region, which consists of equivalent embryonic cells, may be such that the reacting metabolic substances are homogeneously distributed in it. A contemporary chemical theory of morphogenesis envisages the possibility that a reaction system of this kind, in obedience to the laws of physical chemistry and mathematics, and on being activated, can give rise to a patternized distribution of metabolites, e.g. of growth centres, this constituting the chemical basis for the ensuing morphogenetic developments. This general property of the apex is maintained throughout the flora development, however much it may be modified in other ways. It is also known that the positions of new primordia are affected by those already present round the meristem.