Botanical Sketches and Drawings

This sketch and accompanying note represent Leonardo da Vinci's "Rule of Trees," which observes that the total cross-sectional area of a tree's branches at any given height is equal to the cross-sectional area of the main trunk.

Every part of this tree that passes
or from another part through a flat plane?
to become another part along the line of
which will be made above in the line of
of as much perfection as is the perfection of
of that which through the line of that same
height of that same perfection
of that which through every degree of its height
— will be of that same thickness Leonardo is describing his observation that the combined thickness of all branches at a certain height equals the thickness of the trunk below them.