Veins contain both the thick walled xylem vessels which transport water and mineral salts from the roots, and the thinner-walled phloem which transport manufactured food from the leaves. The veins of the leaves are a part of the vascular tissue of the plant. Veins entering the leaf branch repeatedly divide into finer and finer branches before ending among the mesophyll cells. Water and mineral salts carried by the xylem vessels diffuse out to the surrounding mesophyll cells. Sugars produced during photosynthesis diffuse towards the phloem vessels which transport them out of the leaf to the other parts of the plant.