Leaf structure. Coloured scanning electron micrograph SEM of a freeze_fracture through a seedling leaf. The top of the leaf is at bottom. The fracture has revealed the size of the plant cells round, some damaged relative to the thickness of the leaf. Palisade parenchyma tissue is brown and spongy parenchyma tissue is green. This seedling is a dicot, which means that it has two cotyledons the embryonic leaves of a seed. The leaves of a plant contain the chlorophyll by which a plant harnesses the energy of sunlight, using it to make food in the process called photosynthesis.