Morphology and development of the primary and accessory buds of Eucalyptus regnans

Abstract

The vegetative axillary buds of Eucalyptus regnans F. Muell. at various ages were studied by light microscopy in serial sections and by direct observations in the field and glasshouse. All buds (except the very first apical bud) originated from axillary meristems, i.e. from generative tissue which arose in the axils of primordial leaves and survived in a meristematic condition for many years. Each axillary meristem normally produced one emergent primary bud and then an indefinite sequence of concealed accessory buds. The extensive dynamic shoot-system condensed within a primary bud comprised secondary as well as tertiary axes and their respective appendages. All parts were present throughout the year in a continuous sequence of maturation which extended also to the expanding shoot. During winter, development appeared to be merely slowed down or suspended. Primary buds which did not grow into shoots were shed after only a few weeks. The accessory buds were formed in a uniserial descending series at the base of and abaxial to each primary axillary bud. The first of the accessory buds was initiated within the primary bud, and the second within the expanding shoot. The first accessory bud resembled young primary buds in structure, but subsequent accessory buds were less and less complex. Keeping pace with the cambium, the axillary meristem formed a radial trace of thick-walled parenchyma in the wood and accessory buds embedded in a strand of thin-walled parenchyma in the bark. The distal portions of the bud strand and the buds embedded in it were shed progressively with the decorticating bark. Each of the bud strands which traversed the bark of 20-year-old E. viminalis Labill. was found to contain six to 12 radial strips of meristematic tissue. When epicormic growth was stimulated, several of these strips produced files of separate, new, condensed shoots. Of the scores of shoots thus initiated throughout the length of the bud strand, up to 10 or 20 of the distal ones emerged from the bark and grew into epicormic shoots. The buds of 20 other eucalypt species were examined by dissecting microscope only. It appeared that their bud systems were essentially similar to that of E. regnans. The widened concept of the axillary meristem shifts attention from individual buds to the continuous generative powers of the axillary meristem and helps to explain the outstanding capacity of the eucalypts to produce new shoots.

Bud structure and resprouting in coppiced stools of Salix viminalis L., S. eriocephala Michx., and S. amygdaloides Anders

“…Other ways of developing lateral buds in deciduous trees are by branching from the scale axis of a dormant bud (Hahne 1926) or superposed additional buds may develop from the same axillary meristem as the main bud (Chattaway 1958;Cremer 1972). In eucalypts (Eucalyptus sp), the ability to form daughter buds explains the prolific sprouting in some species (Carrodus and Blake 1970).…”

Fitness and evolution of resprouters in relation to fire

“…Depending on the severity of the fire, plants resprout from buds located in the leaf axils of twigs (axillary buds, Cremer 1972) or sunken accessory buds on main stems (epicormic strands/buds, Burrows 2002) or rootstocks (lignotuberous buds, Chattaway 1958). Resprouting may also occur from primary axillary buds on rhizomes (Witkowski and Lamont 1997) or adventitious buds on lateral roots (Lamont and Barrett 1988) or swollen stems (Klimešomá and Klimeš 2007).…”

Branch apices, heterochrony, and inflorescence morphology in some mimosoid legumes (Leguminosae: Mimosoideae)

“…It has been studied in the context of epiphyllous inflorescences (e.g., Dickison 1978;Dickison & Sattler 1974;Sattler 1975a), roots (Yamashita 1970, 1972, and leaves (Sattler & Maier 1977). Sattler (1975b) provided a generalized discussion, and later (1978) examined heterotopy in the context of fusion and floral morphology.…”

“…No matter how many buds are formed, however, the meristematic region remains in the axil. Cremer (1972) calls this an axillary meristem.…”