Modern skyscrapers seem to be constructions solely of concrete and glass. Windows provide the maximum of light for the minimum of weight, and modern developments such as tinted glass diffuse the light to acceptable levels. But plants had learned the benefit of windows long before the days of office blocks.
Fenestaria, a plant of the South African desert, grows mostly underground with only a small window of translucent cells on the surface. The cells are of two types - those that block harmful ultraviolet rays, and those that diffuse the light to a workable level for the green photosynthetic tissue, the part that uses sunlight to produce food.