This small experiment will help to see how water is transported in plants.
The leaves and stalk of the celery standing in the clear water are green. The stalk taken from the blue water has bluish-colored leaves, and tiny blue tripes can be seen running down its entire length beneath the surface. Sections cut from both stalks have a single row of tiny dots near one outer edge. These dots are blue in the section cut from the stalk that was in the blue water. The surfaces of the cross sections cut at the top and bottom of the same stalk are similar.
The cross sections of the celery stalk revealed that the colored water rose from the bottom of the stalk through tiny tube like structures to the top of the stalk. These water-carrying vessels in plants are called xylem tubes. The blue food coloring stains the thick walls of the xylem tubes, so they appear as blue circles on the cross sections. In nature, xylem tubes transport a liquid mixture of water, sugars, and minerals up to the leaves of the plant. This watery mixture is called sap.