The Phactor has spent a lot of time looking at the patterns veins, vascular bundles, make in leaves. The earliest leafy organs of land lacked vascular tissue completely. The earliest land plants were leafless. Then the clubmosses developed leaves with a single vascular bundle down the middle, which limited the width of the blade to the distance water could diffuse from cell to cell. The ancestors of ferns and seed plants developed leaves from modified branches and the venation, the pattern of vascular bundles formed a spreading dichotomy as each bundle branched and branched again right out to the edge of the leaf allowing for a broad leaf, but such veins are not interconnected like the leaves of flowering plants. Ginkgo, a lot of ferns, and cycads have open dichotomous venation still. But the flowering plants have a wholly different pattern, one of looping interconnected veins, so what is their advantage? The answer makes sense; if a vein gets damaged, a looping interconnected network allows materials to be conducted around the obstruction. The leaf shown here shows how translocation continues around the the leaf even after the midvein is injured (dark green dot). Now if only interstate engineers could figure out something similar. Actually some of that pattern does remind me of the Dan Ryan what with obstructions and then suddenly losing a lane! Scary.