False colour scanning electron micrograph of open stomata on the surface of a tobacco leaf Nicotiana tabacum. Stomata are breathing pores scattered over the leaf surface, & sometimes stem, that regulate the exchange of gases between the leaf's interior & the atmosphere. Stomatal closure is a natural response to darkness or drought as a means of conserving water. Each pore is controlled by the turgor of two guard cells on either side; when the guard cells are full of water the pore is open; when they lose turgor, the pore closes. The jigsaw puzzle layer corresponds to the cells of the leaf epidermis. Magnification: X 257 at 35mm size. Original is BW print b745/170.