Cells surrounding the vascular bundle are called the bundle sheath cells. The cells present between the upper and lower epidermis are called the mesophyll cells. In $C _{4}$ plants the fixation of carbon happens in the mesophyll cells, whereas the $C _{3}$ cycle or Calvin cycle occurs in the bundle sheath. This way, the $C _{4}$ plants are able to reduce the water loss due to transpiration. Diagrammatic representation of the $C _{4}$ cycle is shown below.
The cells present in the epidermis of the monocot leaves that store water are called bulliform cells.
The companion cells are specialized parenchymatous cells which are part of phloem.
