noun, plural: mesophyll layers
The leaf is the plant organ chiefly responsible for conducting photosynthesis. In vascular plants, the major tissues that comprise the leaf are the epidermis, the vascular tissues, and the mesophyll tissues. The epidermis is the outermost layer of the leaf. It covers the upper and lower surfaces of the leaf, thus, forming two epidermal layers: the upper epidermis and the lower epidermis. In between these two epidermal layers is a tissue layer comprised chiefly of chlorenchyma cells. This layer is referred to as the mesophyll layer. The vascular tissues can be seen in the mesophyll layer (particularly in the spongy part of the mesophyll layer).
The mesophyll layer is the layer of the leaf comprised of chlorenchyma cells. Chlorenchyma cells are paranchyma cells that are photosynthetic. The chlorenchyma cells have numerous chloroplasts.
Most flowering plants and ferns have a mesophyll layer divided into two sublayers: (1) palisade layer and (2) spongy layer. The palisade layer is the upper part of the mesophyll. It is comprised of vertically elongated cells. The spongy layer is located beneath the palisade layer. Compared with the palisade layer, the spongy layer is spongy in a way that the cells are not so tightly packed, resulting in large intercellular air spaces between them.