Fig. 10.

As a result of branching, sibling axes succeed topologically from a parent axis. This spatial succession is referred to as ‘branching order’ (BO). The first axis (branching order one, BO1) bears a lateral one (branching order 2, BO2) and so on as illustrated diagrammatically for a monopodial branching system (A). In a sympodial branching system, the branching order may increase rapidly (C). When successive sympodial units (each resulting from the functioning of a single meristem) are more or less in a rectilinear disposition (B), it can be considered that the general spatial direction of such a succession constitutes an ‘apparent branching order’ (AO) as in a monopodial system (pseudomonopodium sensu Troll, 1937). x, apical mortality; AOx, ‘apparent branching order’ number x.