How leaves and branches attach and fork on a tree
A branch keeps a third of its girth at each leaf-node; forks rise in youth, hollow in age; the walnut's sevenfold leaf
A leaf from the sixth book of the Treatise on Painting, on the ramification of trees. The text works out the geometry of a leaf attaching to a branch p b c across the span b o c, a third of the branch's thickness, with o the bud from which a branchlet springs, and shows that as the branch thickens to h g s it still occupies a third of the circle. Two further chapters state that the ridges at branch forks are raised in youth and hollow in old age, and that the leaves of the outermost twigs are more evident above than below, most of all in the walnut whose leaf is made of seven leaflets. A ring-shaped cross-section diagram and a drawing of a young branch fork accompany the text, alongside the running head, folio number, and short captions that are not part of the transcription.
On this page
A leaf encircles a third of the branch, and the branch keeps that proportion as it grows
Let p b c be the thickness of the branch and b c d the leaf attaching over the span b o c, which is a third of the branch's thickness, with o the eye or bud where the branchlet is born above the leaf. As the branch grows to the thickness h g s, the attachment still occupies a third of the circle, marked at g s.
Branches born lower on the tree are more curved
That branch will be more curved in the tree which is born lower down in the extent of its ramification.
Fork ridges are raised in youth and hollow in old age
The ridges that form the junction where branches attach together, when they thicken at the forks, remain much raised in the time of youth and remain hollow in old age.
Outer leaves show more above than below, as in the sevenfold walnut leaf
The leaves composing the last ramifications are more evident on the upper parts than the lower, and this happens more in walnut trees than in others, because their leaves are composed of seven other leaves, in the manner shown in the margin a.
Drawing of a young branch fork with a raised junction
A shaded pen drawing shows the forking base of a young stem, its two limbs meeting at a swollen, raised junction, illustrating the claim that fork ridges stand proud while the plant is young.