Plants that are adapted to dry tropical regions have the ${\mathrm{C}}_4$ pathway. Though these plants have the oxaloacetic acid as the first $\mathrm{C}{\mathrm{O}}_2$ fixation product, they use the ${\mathrm{C}}_3$ pathway or the Calvin cycle as the main biosynthetic pathway. Since this is discovered by Hatch and Slack, it is known as Hatch and slack pathway.