Apical dominance

[1] Apical dominance occurs when the shoot apex inhibits the growth of lateral buds so that the plant may grow vertically.

Auxin is predominantly produced in the growing shoot apex and is transported throughout the plant via the phloem and diffuses into lateral buds which prevents elongation.

[1] More simply stated, lateral bud formation is inhibited by the shoot apical meristem (SAM).

The shoot tip rising from the SAM inhibits the growth of the lateral bud by repressing auxin.

Often, lateral dominance can be triggered by decapitating the SAM or artificially decreasing the concentration of auxin in plant tissues.

The principle of apical dominance is manipulated for espalier creation, hedge building, or artistic sculptures called topiary.

Many conifers show particularly strong apical dominance, strongest of all being in the family Araucariaceae , showing a single erect central trunk with strongly differentiated horizontal branching. Cuttings of Araucariaceae species taken from a side branch will not develop erect growth. Araucaria heterophylla , New Zealand.
Weeping larch showing growth habit lacking apical dominance
When apical meristems (apical buds) are continually removed, the shape of a tree or shrub can be manipulated remarkably, because newer, uninhibited, branches grow en masse almost anywhere on the tree or shrub.
Topiary garden, Beckley Park manor, UK