In $\mathrm{C}_4$ plant internal structure of leaf possess special type of anatomy called 'Kranz' anatomy. 'Kranz' means 'wreath' and is a reflection of arrangement of cells. The bundle sheath cells may form several layers around the vascular bundles; they are characterised by having large number of chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces. While in $\mathrm{C}_3$ plants, there is no special type of leaf anatomy. There is only a single type of chloroplast in $\mathrm{C}_3$ i.e. granal, while in $\mathrm{C}_4$ chloroplasts are dimorphic, i.e, granal in the mesophyll cells and agranal in the bundle sheath cells.