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

Buds of shoots from the trunk, main branches, secondary branches and short branches of 10-21 year-old Nothofagus pumilio trees were dissected and thei r contents recorded. The number of differentiated nodes in buds was compare d with the number of nodes of sibling shoots developed at equivalent positi ons during the following growing season. Axillary buds generally had four c ataphylls, irrespective of bud position in the tree, whereas terminal buds had up to two cataphylls. There were more nodes in terminal buds, and the m ost distal axillary buds, of trunk shoots than in more proximal buds of tru nk shoots, and in all buds of shoots at all other positions. The highest nu mber 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 larges t 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 parti cular parent shoot resulted from differences in: (1) the number of differen tiated organs in the buds; (2) the probability of differentiation of additi onal organs during sibling shoot extension; (3) sibling shoot length; (4) s ibling shoot diameter; and (5) the death of the apex and the most distal le aves of each sibling shoot. (C) 2000 Annals of Botany Company.