In addition to water, carbon dioxide, mineral salts, and heat, light is one of the factors which are of vital importance for the green plant. It provides energy for the photosynthesis and brings about the growth and development of plant forms. In addition to the light on itself, also the light intensity plays an important role. The leaves of deciduous trees are the place where the energy required for the plant is formed by photosynthesis and assimilation. This is done in the chlorophyll-containing cells of the palisade layer. There below is loose fill and aerenchyma tissue. Outwardly a leaf is sealed off by a layer of epidermal cells, the outer walls thereof are thickened.
In fact, the light influences the construction of the plant and its leaves. We find sun leaves on the outer edge of the crown and on the south side of it, shade leaves
inside the crown and on the north side (this applies to the northern hemisphere) They show characteristics of sun and shade plants. In order to get a maximum amount of light, they put their leaf surface perpendicular to the incident light.
Sun leaves are thicker because their assimilation tissue, the palisade parenchyma, which has longer cylindrical cells, often lying close together in double rows. They contain numerous chloroplasts that lie along the long sides.
In the palisade parenchyma of the shade leaves however, there are shorter cells loosely standing next to each other in a single row. Their shape approximates that of the cells of the spongy parenchyma of the ventilation tissue. They also have less chloroplasts. In terms of volume, the intercellular spaces of the shade leaves are larger than that of the sun leaves, this in order to provide the cells with sufficient carbon dioxide at the lower possible exposure to light. Shadow leaves are larger and light green, sun leaves are small and dark green because of the numerous chloroplasts.