Guard cells are located in the leaf epidermis and pairs of guard cells surround and form stomatal pores, which regulate CO2 influx from the atmosphere into the leaves for photosynthetic carbon fixation.
Stomatal guard cells also regulate water loss of plants via transpiration to the atmosphere.
Vascular tissue composed of xylem<span> (red) and </span>phloem<span> tissue (green, between the</span>xylem<span> and </span>cortex<span>) surrounds the pith. Collenchyma cells are elongated cells with unevenly-thickened walls . They provide structural support, mainly to the stem and leaves.</span>
