VIII. Botany for Painters and Elements of Landscape Painting: 397.
397.
There is no boss on branches which has not been produced by some branch which has failed.
The lower shoots on the branches of trees grow more than the upper ones and this occurs only because the sap that nourishes them, being heavy, tends downwards more than upwards; and again, because those [branches] which grow downwards turn away from the shade which exists towards the centre of the plant. The older the branches are, the greater is the difference between their upper and their lower shoots and in those dating from the same year or epoch.