Leaf Arrangement and the Angles of Branches
Why the sixth leaf sits above the first, and why the youngest shoots fork more sharply
Under the running head SESTA, this leaf of the Treatise on Painting sets out Leonardo's rules for how leaves and branches grow. The angles of the branchings are more acute in the younger part of the tree; a branch's thickness diminishes from leaf to leaf only by the thickness of the bud it sheds; and nature places the sixth leaf above the first for two reasons, so that rainwater can run down to feed each bud and so that new branches, turned to five aspects, do not shade one another. A faint pen sketch of a forking twig sits within the text column.
On this page
On the birth of leaves on their branches (a): the rule of the sixth leaf
Nature sets the leaves of the outermost branches so that the sixth leaf always stands above the first, following in succession. This serves two ends: rainwater lodging in the hollow at a leaf's base runs down to nourish the bud, and the five branches, born turned to five aspects with the sixth far above the first, never cover one another.
Branch thickness lost at each bud
The thickness of any branch never diminishes across the span from one leaf to the next, except by as much as the thickness of the bud sitting on that leaf. That amount of thickness is what the continuing branch lacks as it runs on to the next leaf.
Pen sketch of a forking twig
A light, sketchy pen drawing occupies the middle of the text column, showing a slender branch with a shoot or bud springing from it. It illustrates the described junction of leaf, bud, and continuing branch rather than any labelled figure.