Comment concerning Leonardo's rule
  In this comment we propose a novel explanation for the Leonardo's rule concerning the tree branching. According to Leonardo's notebooks he observed that if one observes the branches of a tree, the squared radius of the principal branch is equal to the sum of the squared radius of the branch daughters. 
O. Sotolongo-Costa, L.M. Gaggero-Sager, T. Oseguera-Manzanilla and   D.S. D\'iaz-Guerrero
physics.bio-ph