1 . The leaf blade of 43 species of the Gramineae were investigated histologically on the degree of development of motor cells and the unevenness on the surface of leaf blade. 2 . Degree of development of motor cells were greater in C, plants than C3 plants. Motor cells in C3 plants were non-development or almost undevelopment. 3 . The surface of leaf blade was comparatively flat or somewhat uneven in C, plants as compared with that of C3 plants having a tendency to be markedly uneven. (Received July 1, 1974 )