Fig. 30.

Morphogenetic gradients and physiological age of meristems (after Barthélémy et al.,1997a). Theoretical and diagrammatic representation of the distribution of elementary botanical entities with similar characteristics (i.e. presenting the same ‘physiological age’ and represented by the same size and colour rectangle on the diagram) according to some main morphogenetic gradients very commonly observed in seed plants: for the initial structure and reiterated complexes four ‘branching orders’ (BO1–BO4), BO1 representing the main axis; ‘base effect’ is a gradient linked to the ‘establishment growth phase’ of any plant grown from seed; ‘acrotony’, with increasing acropetal gradient of vigour of lateral axes, is a common feature of the annual shoots and growth units of most rhythmically growing trees; ‘drift’ is a general feature linked with axis ageing; sequential ‘reiteration’, in this case, represented by the automatic duplication of the sequence of development and associated gradients of the main axis by another axis.