Spongy mesophyll tissue has been discovered preserved in fossil leaf compressions. The fossils occur in an outcrop at Genesee, Alberta, Canada. The fossiliferous beds belong to the Edmonton formation of Upper Cretaceous-lower Tertiary age. The mesophyll characteristic, when taken in conjunction with other characteristics, was found useful in the identification of some fossil leaves. Numerous detailed observations as well as comparisons of both living and fossil leaves show that the remains represent neither the epidermal nor the palisade tissue.