The principle parts of the leaf incorporate the leaf base, petiole, and lamina. The upward segment of a dorsiventral leaf through the lamina shows three principle parts, specifically, epidermis, mesophyll and vascular framework. The epidermis which covers both the upper surface (adaxial epidermis) and lower surface (abaxial epidermis) of the leaf has obvious fingernail skin. The abaxial epidermis by and large bears more stomata than the adaxial epidermis. The last may even need stomata. The tissue between the upper and the lower epidermis is known as the mesophyll.
The well-labeled diagram of the internal structure of the leaf is given below: