If you slice into a stalk of celery, you will be able to see vascular bundles that carry water, nutrients and hormones throughout the plant. These vascular bundles, or veins, are made up of the xylem and phloem.
The xylem mostly carries water. Xylem is Greek for wood, so an easy way to remember the word meaning is to think “water wood”. The xylem also carries some mineral salts, but that is mostly the job of the phloem. Generally, the xylem is found closer to the center of a stem, while the phloem is closer to the outer edge.
The most interesting thing about the xylem is that it pulls water upward from the ground, against gravity. If you’ve ever picked up a bucket full of water, you know this isn’t always easy. There is some debate about how this actually occurs, but most botanists agree that it has a lot to do with surface tension.
Water molecules like to stick together. As a plant breaths, evapotranspiration occurs, reducing the amount of water in the leaves and stem. The water in the ground in then pulled upward by the water in the above ground portion of the plant. The structure of the xylem helps support the water molecules as they are drawn up.
Xylem vessels are actually made up of elongated cells that are dead. Weird, right? These cells are arranged end to end, with little openings between each cell. There are secondary xylem cells that contain lignin. Lignin is found in cell walls and it is what holds plants upright.
Diseases of the xylem include Fusarium wilt, root rot, damping off, and tomato spotted wilt.
Children's activity: This is crazy easy and the kids seem to really enjoy it. Simply take several celery stalks and place them in separate cups or glasses. To each cup, add some water and a few drops of a specific food coloring. As the stalks pull the water up, they bring the dye too, and the color changes can be striking. (It works faster if you trim the base of each stalk to create fresh openings for the vascular tissue.)
You can grow a surprising amount of food in your own yard. Ask me how!
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