A scanning electron micrograph of the leaf surface of a garden Zinnia. The picture shows interlocking epidermal cells (green) with pairs of stomatal guard cells in yellow. The epidermis protects the leaf contents from water loss. It is covered with a cuticle, (and on some plants, a layer of wax). The leaf interior - the mesophyll - is the main site of photosynthesis. It requires light, moisture and air. Moisture inside the leaf comes from the soil via the plant roots. The air enters through stomata in the epidermal surface. In this picture, each yellow area is comprised of a pair of guard cells. The wall between the guard cells can part to become a open pore, allowing air to enter the leaf. All the pores visible here are closed, and appear as a line in the centre of the yellow areas. The pores close at night, and - to conserve water - when the soil is dry. Mag x150 at 10x8