Fig. 6.

Stem extension may occur more than once during a same calendar year. The set of growth units produced in one year is then called an annual shoot (A.S.). In Quercus ilex (A) or Pinus halepensis (B) bicyclic shoots, the first growth unit (G.U.1) may produce reproductive organs whereas the second (G.U.2) is vegetative. On old stems, the presence of female cones or fruits on the first growth unit and the major development of branches borne on the second growth unit of such bicyclic annual shoots distinguishes these first and second growth units, respectively, as the a posteriori delimitation of successive annual shoots (B). ‘n-1’, ‘n’, ‘n + 1’, successive theoretical years of growth; solid white arrow, limit of an annual shoot; dashed white arrow, limit of a growth unit.