Celery. Light micrograph of a thinly sliced section across a celery (Apium graveolens) stem. An outer layer (dark green) surrounds the soft watery interior. A semi-circle of vascular bundles (light and dark green ovals) supports the stem. These bundles contain xylem (holes in dark green tissue) and phloem (light green) tissue that carry water & minerals, and nutrients respectively. The phloem lies on the outer edges of the vascular bundles, between the xylem and the fibrous strands (collenchyma tissue) that run down the stem surface. These structures make up the stringy part of celery. Combined brightfield and darkfield illumination. Magnification: x10 at 6x7cm size.