Leonardo da Vinci is a name synonymous with the Renaissance, remarkable for his contributions to art, engineering, and anatomy. But did you know that this prodigious polymath also dipped his toes into the realm of botany? Among Leonardo’s “Codex” lies an observation that’s come to be known as “Leonardo da Vinci’s rule of trees.” Simply put, this rule posits that the total cross-sectional area of a tree’s branches is equal to the cross-sectional area of its trunk. Penned more than 500 years ago, the rule of trees was almost immediately adopted by scientists who were seduced by such an elegant observation. To this day, da Vinci’s rule of trees is still taken by many at face value as true. However, a new study has found that, while valid in some respects, the rule of trees isn’t exactly correct when applied to the internal vascular structures of trees.