Courtesy A. J. Turgeon
This leaf cross section shows the typical anatomy of a grass leaf blade. The upper (adaxial) and lower (abaxial) surfaces are a single layer of epidermal cells. On the adaxial side, a portion of the epidermis may be made up of enlarged, thin-walled cells called bulliform cells. Enclosed within the epidermis are the spongy mesophyll cells which, along with veins, occupy much of the internal volume of the leaf. Finally, the epidermis is permeated by a series of openings, called stomates, through which gaseous exchange between the leaf and the atmosphere can occur. Specialized cells, called guard cells, absorb water and change shape to provide the epidermal openings.