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palissade parenchyma

A layer of columnar cells (generally one to three cells thick) that form the upper layer of a leaf, just below the epidermis. This section of the leaf is particularly adapted to photosynthesis, and contains the highest number of chlorophyll grains. (Not all plants have a palissade parenchyma, like ferns and grasses.)

Fagus sylvatica: vertical section of the leaf

Fagus sylvatica: transverse section through a leaf with palissade parenchyma and spongy parenchyma below.