Mesophyll

This is a picture of a leaf. Mesophyll is the inner tissue of a leaf. It is the middle layer between the upper and lower epidermal layers. The mesophyll layer is composed of parenchyma, or photosynthetic cells with chlorophyll, which explains why it is the site of photosynthesis in leaves. The mesophyll itself is also split into two layers, including palisade mesophyll and spongy mesophyll. The palisade mesophyll layer is the upper part of the mesophyll layer and consists of tightly packed parenchyma cells that function to trap sunlight. In the spongy mesophyll, the cells are more loosely arranged, so that air spaces allow for gas exchange. With the occurrence of photosynthesis, the mesophyll layer is usually filled with gases, including carbon dioxide and oxygen.