The Birth of Leaves on Their Branches
Phyllotaxis: why the sixth leaf grows above the first, and how a branch thins at each bud
Leonardo studies the arrangement and nourishment of leaves on the outermost branches of plants. He observes that a branch loses thickness at each leaf by exactly the width of the bud (the 'eye') set above it, and that nature spaces the leaves so that the sixth stands above the first. This spiral arrangement lets rainwater collect in the hollow at each leaf's base to feed the bud, and keeps next year's branches from shadowing one another. A marginal red-chalk sketch shows the 'eye' or bud lodged in the hollow of a branch.
On this page
A branch thins by the width of the bud above each leaf
The thickness of a branch does not diminish across the span from one leaf to the next except by as much as the thickness of the eye (bud) that sits above that leaf. That is precisely the thickness the branch loses as it continues on toward the following leaf.
The sixth leaf grows above the first (spiral phyllotaxis)
Nature arranges the leaves of the outermost branches so that the sixth leaf always stands above the first, and so on in succession, unless the rule is impeded. This lets rainwater settle in the hollow at each leaf's base and run down to nourish the bud, and it keeps the following year's five branches turned to five different aspects so that none covers another.
The 'eye' or bud in the hollow of the branch
A small marginal figure isolates the bud, the 'eye', set in the concave hollow where a leaf joins its branch. It illustrates the drop of water lodging in that hollow to feed the sprouting bud described in the pen note.