Question

why are stomata present in lower part of leaf in plenty?

Answer 1

It's because the diffusion of gases takes place through the lower part of the leaf......
Hope it helps...
For any more queries message me in inbox..

Answer 2

All surfaces of the leaf have some amount of stomata for regulating gas exchange for photosynthesis. However, the lower epidermis (the underside of the leaf) has more, because it is more often in the shade and so it is cooler, which means evaporation won't take place as much.