Why plant stems curve and thicken toward the south
The sun draws moisture to the sunlit side, so branches grow longer and denser to the south
The leaf carries a red-chalk sketch of a bare tree at the upper right, with the rest of the page written in pen. Leonardo notes that almost all plant stems curve so their convex side faces south, where the branches also grow longer, thicker and denser. He attributes this to the sun drawing moisture toward the plant's nearest surface, and adds that the effect is clearest in dense, pruned plants that regrow every three years, unless neighbouring plants block the sun.
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Southward curving and thickening of plant growth
Almost all plant stems curve so that their convex side faces south, where their branches also grow longer, thicker and denser than toward the north. Leonardo attributes this to the sun drawing moisture toward whichever surface of the plant is nearest to it. He adds that the effect shows most clearly in dense, pruned plants that put out new growth every three years, provided no neighbouring plants block the sun.