VIII. Botany for Painters and Elements of Landscape Painting: 395.
395.
Every year when the boughs of a plant [or tree] have made an end of maturing their growth, they will have made, when put together, a thickness equal to that of the main stem; and at every stage of its ramification you will find the thickness of the said main stem; as: i k, g h, e f, c d, a b, will always be equal to each other; unless the tree is pollard--if so the rule does not hold good.
All the branches have a direction which tends to the centre of the tree m.