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SUMMARY (1) Analysis of more than one-hundred plant species has shown certain consistently-recognizable biological age states in their ontogeny. These are called seed, seedling, juvenile, immature, virginile, reproductive (young, mature and old), subsenile and senile. (2) Each age state may be characterized by a particular combination of quantitative and qualitative features. Qualitative features used to define the various age states are: the manner of nutrition, the type of growth, the pattern of branching of the root and shoot systems, leaf form, the presence of a particular type of shoot, the ability to reproduce by seeds, the balance between living and dead structures, and the balance between actively-growing and fully-formed structures. (3) Quantitative characteristics change uninterruptedly during ontogeny, and as a rule follow a unimodal curve. (4) Age states of species representative of a variety of growth forms have been distinguished and described. These include trees, shrubs, semi-shrubs, low semishrubs, firm- and loose-tussock plants, and the following categories of perennial herbs: long- and short-rhizomed, root-suckering, stoloniferous, bulbous, tuberbulbous, tuberous and tap-rooted. (5) On the basis of these age-state studies, three main types of ontogeny in polycarpic plants are defined, using as characterizing features architectural changes of the individual plant, the form and timing of break-up of the individual plant, and the extent of rejuvenation.
Gatsuk et al. (1980) studied this question.