Why lower tree-branches grow longer than upper ones
Red-chalk study of a bare tree, with notes on branch knobs, downward-flowing sap, and shade
A red-chalk study of a leafless tree, its trunk and spreading limbs drawn at the upper right, accompanied by two notes on how branches grow. Leonardo states that no knob or swelling appears on a branch except where another branch has been lost, and that the lower branchlets of a bough grow more than the upper ones. He explains this by the weight of the nourishing sap, which moves downward more easily than up, and by the fact that lower shoots move away from the shadow cast toward the tree's center. A second note adds that the older the branch, the greater the difference between its upper and lower branchlets, while within a single year's growth the difference is slight.
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Branch knobs and the greater growth of lower branchlets
No knob appears on the branches except where some branch has been lost. The lower branchlets of a bough grow more than the upper ones, because the moisture that nourishes them, having weight, moves more easily downward than upward, and because the lower shoots draw away from the shadow that lies toward the center of the plant.
Age widens the difference between upper and lower shoots
The older the branches are, the greater is the difference between their branchlets above and those below; and in the shoots of the same year that difference is small.
Red-chalk study of a bare tree
A leafless tree is drawn in red chalk, its trunk rising into an open crown of divided limbs. The drawing illustrates the accompanying observations on how branches divide, bend, and vary in length along the trunk.