If you look at the Pines sitting in your balcony you will wonder why they growth taller and taller and their apex moves towards the sky in straight line. You can see apical dominance. What provides apical dominance. Plants produce growth regulators on or near apical regions of roots as well as shoots and transfer it to the basipetal or acropetal pattern down from stem apex and up from root apex by certain mechanism which is highly croordinated using a set of genes which I have not been able to comprehend how do they work using different signal transduction systems.
Let us understand in simple way. If you grow plants in dark they elongate . This elongation is due to non destruction of growth regulators produced at the leaf tips of the plants in dark. The light destroys the growth regulators or reduces their concentrations. Its high concentration of growth regulators at the apex which prevents its growth and apex sends the growth regulators downwards so that the branches are promoted.
Its the behvior of apex like a caring parent which makes their children grow like branches of a tree. Man learns from nature if you share more you grow more.
See below a plant of Cryptomeria japonica with some apical dominance.