The veins of a single leaf

Inside a single leaf runs a net of thick veins branching into fine ones and rejoining. Block one point and water still has a way around. Even the rate at which thickness decreases follows a rule, arranged to spread the widest with the least resistance.

첫째 단서 — 구조Thick veins branch into fine ones, and the fine ones rejoin into a net. Block one point and water still has a way around. It is the arrangement a city road network uses.
둘째 단서 — 목적A leaf takes light and makes food. For that, water must reach the far edge and what is made must travel back down the stem. The venation handles both directions in one net.
셋째 단서 — 질서The branching angles and thicknesses are not arbitrary. The rate at which thickness decreases follows a rule — an arrangement that spreads the widest with the least resistance.

All of this is drawn inside a leaf you can hold in one hand. This is where readings begin to diverge.