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Comparison of Temporal Patterns in Flower Ontogenesis by Means of Normalized-Age Sequences
Annals of Botany
, 1989. V. 64. No. 2. P. 179–183
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A convenient measure of biological and, in special cases, physical age is the plastochron (P) or the plastochron index (PI). The basic concept can be generalized and also be applied to any strictly modular system as well as to its modules. However, differing values will be assigned to modules arising from modular systems of different ‘relative developmental density’. For instance, if one modular system (e.g. a shoot or an infloresence) produces more modules (e.g. leaves or flowers) than an other during development between two independently-defined reference stages, then modules of equal developmental status differ in their plastochronal ages. This problem is avoided by reference to the normalized-age concept, using the ‘normalized-plastochron’ (NP) and the ‘normalized-plastochron index’ (NPI). This concept assigns to a particular stage a fraction of the difference in age of two selected, well-defined, reference stages. The younger reference stage is assigned a value of 0 NP, the older one of 10 NP; stages younger or older are respectively assigned negative values or values greater than 10. The NP- and NPI-concepts permit the construction of a normalized sequence of ontogenesis and, it is hoped, the detection of the temporal patterns of ontogenesis among related species. An example of the application of the scheme of flower development in five species of the Scrophulariaceae is given here.