Vein structure in a Philadelphus coronarius aureus (Golden Mock-orange) leaf.
The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. They are typical examples of pattern formation through ramification. The pattern of the veins is called venation.
The veins are made up of:
Xylem: tubes that brings water and minerals from the roots into the leaf.
Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.
The xylem typically lies over the phloem. Both are embedded in a dense parenchyma tissue, called "pith", with usually some structural collenchyma tissue present.
Description above from Wikipedia article: http://en.wikipedia.org/wiki/Leaf#Veins
Philadelphus coronarius aureus, or Golden Mock-orange, is a cultivar of Philadelphus coronarius. The aureus cultivar has bright golden yellow leaves, and is a popular shrub in gardens.