The leaves of green plants using the C₄ or Hatch-Slack pathway for photosynthetic carbon fixation almost invariably have a specialized internal arrangement of cells surrounding the vascular bundles that is called Kranz anatomy. Kranz, the German word for "halo," or "wreath,"refers to a ring of mesophyll cells just to the outside of another ring of large bundle-sheath cells, both of which encircle the vascular bundle. In transverse sections viewed under the microscope, the two cell layers give the appearance of a wreath surrounding each bundle. In addition to the unique "wreaths," other features that typify leaves with Kranz anatomy include small intercellular spaces, and frequent veins.

Kranz anatomy and the C₄ photosynthetic pathway are especially characteristic of tropical grasses such as sugar cane, where it was first discovered, and corn, although it has also been found in other plants. It is sometimes possible to distinguish...