After the first 15 minutes, describe the cross-section of the thin celery slice. What does it look like? Try to identify the stringy transport bundles of xylem and phloem. What color are they? How does this lab prove vascular tissues carry water and minerals up the stem? After 24 hours, look carefully at the leaves of the celery. What color are they? Explain the change in color of the leaves that you saw.