Leaf veins. Macrophotograph of a leaf from a horse chestnut tree (Aesculus hippocastanum) showing the leaf veins. Running from left to right is the central vein. This contains vascular bundles that transport food (carbohydrates) and water in and out of the leaf. Smaller veins branch diagonally off the main vein and these in turn branch into finer vessels, creating an elaborate network. This branching arrangement distinguishes dicotyledonous flowering plants from the monocotyledons, which have narrow leaves and parallel veins.