Leaves and the Environment
Sun and shade leaves. The architecture of leaves changes depending upon the light intensity in which they grow, even on the same plant. Sun leaves usually are smaller and thicker with more and better defined palisade cells, and more chloroplasts. They frequently have more hairs as well. Sun leaves rarely have chloroplasts in their epidermal cells, but chloroplasts are common in the epidermises of shade leaves.
Day length. The presence or absence of light (as well as particular wavelengths) influences the production of plant hormones and the development of plant organs. For example, leaves do not develop normally in the dark, and chloroplasts don't turn green unless exposed to light; the tissues are yellow and said to be etiolated. The duration of the light also influences the shape of many kinds of leaves; leaves produced during the short days of spring are different from those produced during the long days of summer.
The presence or absence of water in the environment has profound effects on the structure of plant stems, roots, and leaves, so much so that three types of plants are recognized based on the water content of the soil: xerophytes, mesophytes, and hydrophytes. In this categorization, the common plants, mesophytes, live where water is neither abundant nor limited, i.e. in a mesic (meaning middle) environment. Xerophytes (xeric meaning dry) are adapted for life in arid regions while hydrophytes (hydric meaning water) live in water or else have their roots in wet soil. While it is tempting to attribute structural adaptation to one factor of the environment alone, in truth, all of the physical and biological factors of the environment undoubtedly contribute. Because of the role of water in plant metabolism, however, water and its availability clearly control the structures as well as the functioning of plants.