Anatomy of Monocot Leaf - Grass

A grass leaf - the monocot comparison - keeps the same three tissue systems but rearranges them noticeably compared with a dorsiventral dicot leaf. Its upper and lower epidermis are both single layers of thin-walled cells under a thick cuticle, with roughly equal numbers of stomata on each face (unlike the lower-surface bias typical of dicot leaves); each stoma is flanked by dumb-bell-shaped guard cells (the chloroplast-bearing cells that actually control the pore) plus distinct subsidiary cells. The upper epidermis additionally carries two specialised cell types not found in a typical dicot leaf: large, thin-walled bulliform (motor) cells, which change turgor to roll and unroll the leaf blade in response to water stress, and silica cells, filled with silica deposits. Between the two epidermal layers, the mesophyll breaks from the dicot pattern most sharply of all - it is not differentiated into palisade and spongy regions; instead every mesophyll cell is nearly isodiametric, thin-walled and compactly packed, with no consistent top-to-bottom asymmetry. The vascular bundles running through this uniform mesophyll are, like a dicot leaf's veins, conjoint, collateral and closed. Beyond ordinary stomata, some leaf margins (in plants grown in constantly moist, shaded conditions) instead carry hydathodes - pores permanently open (rather than actively regulated by guard cells) and ringed by cuticularised cells rather than subsidiary cells, through which the plant performs guttation, exuding liquid water under root pressure rather than losing water vapour by transpiration. A related, unrelated-to-leaf-anatom …