An anatomical study of epicormic bud strand structure in Eucalyptus cladocalyx (Myrtaceae)

Epicormic bud strands in Eucalyptus cladocalyx F. Muell. extended from the pith to the outer bark. In large-diameter stems (30 cm diameter, 2 cm bark thickness) the epicormic bud strands had their greatest anatomical complexity at the level of the vascular cambium. At this level the epicormic bud strand was about 3 mm wide x 5 mm high in transverse section and within it were 22 40 radially arranged strips of cells of meristematic appearance embedded in a mainly parenchymatous matrix. Well-developed buds with leaf primordia and vascular connections were never observed in intact trees, although when stimulated each meristem strip could produce numerous bud primordia. Toward the bark surface the epicormic bud strands became progressively simpler in structure. On the stem surface, the position of the epicormic bud strand was shown by a number of adjacent small protrusions which appeared to have no meristematic potential. From the outer secondary xylem to the pith the bud strand usually became slightly smaller in diameter and its cells, although nucleated, had thick lignified walls and the meristem strips were much reduced or were not present. In most previously investigated angiosperm tree genera epicormic shoots develop from suppressed buds embedded in the bark. Eucalyptus appears to be unique in that suppressed buds are not present in the bark and that each epicormic bud strand has the potential to form numerous bud primordia when stimulated to do so.