Mesophyll tissue is present in leaves. It is the tissue located between the upper and lower epidermis of a leaf and is the primary site of photosynthesis.

The mesophyll is composed of two types of cells:

• Palisade mesophyll: These cells are elongated and tightly packed, located just below the upper epidermis. They contain a high concentration of chloroplasts.
• Spongy mesophyll: These cells are more irregularly shaped and loosely packed, with large air spaces between them, which facilitate gas exchange.

Source:

• Britannica - Mesophyll