C4 plants are characterised by Kranz anatomy. C4 pathway of photosynthesis was discovered by Hatch and Slack. (1965). In C4 plants the CO2 combines with phosphoenol pyruvate (PEP) to form a 4-C compound oxaloacetic acid (Hence, named C4 plant). It is the first product of C4 cycle. On the other hand in C3 plants the CO2 combines with ribulose 1-5, diphosphate to form the 3-C-compound phosphoglyceric acid. It is the first stable product of C3 plants.