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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, firmand 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.
