Leaf surface. Coloured scanning electron micrograph (SEM) of the surface of a decaying leaf. The individual cell layers within the leaf surface have begun to decompose. Here the outermost layer, the epidermis (green, centre right), has detached from the underlying tissue and is standing upright. In a healthy leaf the epidermis protects the plant tissues from excessive water loss and from infection by some plant pathogens. Magnification: x500 at 6x6cm size.