Bud content and its relation to shoot size and structure in Nothofagus pumilio (Poepp. et Endl.) Krasser (Nothofagaceae)

42 ref.International audienceBuds of shoots from the trunk, main branches, secondary branches and short branches of 10–21 year-old Nothofagus pumilio trees were dissected and their contents recorded. The number of differentiated nodes in buds was compared with the number of nodes of sibling shoots developed at equivalent positions during the following growing season. Axillary buds generally had four cataphylls, irrespective of bud position in the tree, whereas terminal buds had up to two cataphylls. There were more nodes in terminal buds, and the most distal axillary buds, of trunk shoots than in more proximal buds of trunk shoots, and in all buds of shoots at all other positions. The highest number of nodes in the embryonic shoot of a bud varied between 15 and 20. All shoots had proximal lateral buds containing an embryonic shoot with seven nodes, four with cataphylls and three with green leaf primordia. The largest trunk, and main branch, shoots were made up of a preformed portion and a neoformed portion; all other shoots were entirely preformed. In N. pumilio , the acropetally-increasing size of the sibling shoots derived from a particular parent shoot resulted from differences in: (1) the number of differentiated organs in the buds; (2) the probability of differentiation of additional organs during sibling shoot extension; (3) sibling shoot length; (4) sibling shoot diameter; and (5) the death of the apex and the most distal leaves of each sibling shoo