Conservation of Branch-Thickness; Opposite vs. Alternate Boughs
Each year's branches together equal the parent bough; leaves and branches change place in season
This leaf completes the rule that a plant's yearly branches, once grown, together equal in thickness the parent branch that bore them, illustrated with a small fork where a d and b d joined equal branch d c. A new section (828) notes that boughs shift position between winter and their summer load of leaves and fruit, and that thickness passes almost imperceptibly from branch to branch. Leonardo distinguishes two arrangements of branches, opposite or alternate: alternate branching makes the central stem bend from side to side, opposite branching keeps it straight, shown by two sapling diagrams. He adds that a branch, and likewise a fruit, always springs above the scar of a leaf.
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The last branches a d + b d equal their parent d c
Each year the branches a plant gains, once fully grown, together equal in thickness the branch born the year before that produced them. So the outermost branches a d and b d, joined together, equal the branch d c that gave them birth; the thickness passes almost imperceptibly from fork to fork.
Opposite or alternate branching (h)
Branches are set in two ways: opposite one another, or not. If they are not opposite, the middle stem bends now toward one branch, now the other; if they are opposite, the central trunk stays straight.
A branch springs above each leaf-scar (i)
The branch is always generated above the attachment of the leaf, and the fruit does likewise. Branchings also change their position between winter and the season when they load with leaves and fruit.