These are images of veins from a celery stalk, taken by Zoe Schnepp using an optical microscope. The veins were first stained by standing the celery stalk in blue dye. The coil-like structures are part of the walls of the veins (xylem), strengthening them against the large capillary forces of the water inside.
The helical xylem are even clearer when you look at a piece of celery using a scanning electron microscope.
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