XVI International Botanical Congess

The indeterminate growth of higher plants causes various forms of pattern repetition. Special interest is given on those repetitions that point to the expression of identical developmental genes on primordia of different complexity. Examples from inflorescence morphology illustrate that structural patterns are determined by three criteria: the position of the meristem concerned, the developmental pathway resulting in the specific appearance of the adult structure, and the time of gene expression defining the degree of complexity. All aspects are influenced by ontogenetic abbreviations which appear to stimulate most variations. In view of the complementary equality of the three findings `homotopy , `homoplasticity and `homochrony the dominant role of the positional criterion in comparing structures is questionable.