Stomal complex. Coloured transmission electron micrograph (TEM) of a stomatal (pore) complex in the young leaf of the pea plant (Pisum sativum). Two developing guard cells (blue) are separated by a cell wall (orange) that will split to form the stomatal opening. Both cells are dominated by a large nucleus (yellow) containing clumps of chromatin (red). The stomata regulate the exchange of water and gases between the atmosphere and the leaf interior. Stomata open when the guard cells are full of water and close when they are not. Closure is a natural response to darkness and drought. Magnification: x5200 at 10 centimetres high.