What is the difference between Palisade and Spongy mesophyll? 

Palisade Mesophyll cells: They are found inside the mesophyll tissue of dicot plants. These cells contain maximum number of chloroplast which is the primary site of photosynthesis. Palisade cells are cylindrical in shape and form a dense, compact layer.

Spongy Mesophyll cells: They are located just beneath the palisade layers in mesophyll tissue. They contain few chloroplasts and the spongy layer is not that dense or compact like a palisade. The cells are round in shape and contain air spaces within. The gases can move through these air spaces.