Roots soak up water from the soil, but not everything in the soil is good for a plant. A ring of gatekeeper cells decides what gets into the plant's pipes.
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If you sliced across a root, you would see the plant's water and sugar pipes bundled in the center. Wrapped around that center is a single ring of cells called the endodermis.
Each endodermal cell has a special band in its side walls called the Casparian strip. It is made of waxy, waterproof materials. It goes all the way around each cell, like a belt.
The Casparian strip is named after Robert Caspary, a scientist who described it in the 1800s.
Water from the soil can seep through the spaces between root cells, like water through a sponge. But when it reaches the endodermis, the waterproof belts block that sneaky path.
Press Water goes in on the 3D model and watch water pass through an endodermal cell to reach the center.