Abstract

The growth activity of an organ (variable y) is defined simultaneously by the instantaneous absolute ratedy/dt and its variationd 2y/dt2. The use of these two descriptors allows a sigmoidal (i.e. continuous and non periodical, as observed for the logistic function) growth curve to be discretized into a series of 5 growth states or phases which are delimited by the following singular values: max, Vmax (=0), max, adult stage. The (V, ) plot, termedgrowth trajectory, visualizes, e.g. in the case of Richards-Nelder's generalized logistics, the unequal duration of these phases and allows the dissymmetry property of the growth function to be characterized precisely.At a more integrated organization level, such anorganic series (e. g. the set of the leaves borne by a same branch), the above concepts allow two kinds of analyses to be carried out: (i) in thekinetic approach, the growth trajectory of the series can characterizes, under certain conditions, the emergence of a new property: theoccurrence of growth activity rhythms which are independent of meristem dormancy processes; (ii) thedemographic approach shows thegrowth structure of the phytomer population (a particular form of age structure) and the associated dimensional structure (plant partition into zones or regions in relation to the growth state of the various phytomers).