The upper layer of leaf tissue consisting of tightly packed, column-shaped cells rich in chloroplasts that conduct most of the leaf's photosynthesis. These cells are arranged perpendicular to the leaf surface to maximize light capture.
From French 'palissade' (fence of stakes) describing the orderly, upright arrangement of cells, combined with Greek 'mesos' (middle) and 'phyllon' (leaf). The term was coined in the 19th century as plant anatomy became more detailed.
Palisade mesophyll cells are arranged like a solar panel array, with each cell positioned to catch maximum sunlight! They're so packed with chloroplasts that they can contain up to 70% of a leaf's total chloroplasts despite being just one layer thick.
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