Transpiration in celery. Celery (Apium graveolens) stalks with some leaves are placed in two glasses that contain water with red and green food coloring (left frame). After one day, celery acquires apparent red and green tint, respectively (right frame). In plants, water and nutrients (and dyes, in this demonstration) are moved up the xylem due to capillary action and water potential difference. The process of water movement through a plant and its evaporation from aerial parts is called transpiration.