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  • Fern sorus x100. You can see stalked sporangea, each with a row of thickened spring-like cells in the sporangium wall called an annulus. When the annulus drys out and contracts, the sporangium will rip open at the area indicated.
  • Cryptomarium falcatum sorus x30. Located on the lower surface of a leaflet (pinnule), the sorus is protected from premature drying by an indusium which covers the sproangia.
  • Gleichenia rhizome xs x20. Primary xylem is in the center surrounded by phloem and cortex.
  • Pteridium rhizome xs x12. Plates of xylem are each surrounded by phloem.
  • Fern gametophyte x12. The dark round structures are antheridia or archegonia.
  • Antheridium x400. This is the gametophyte's male sex organ. Each has a single layer of cells containing coiled sperm. Antheridia are located at the margins of or on the lower center of gametophytes.
  • Fern archegonium x400. These female sex organs are near the center of the lower gametophyte surface. Each has a neck, a neck canal (both easily visible in the illustration) and an egg at the base. Sperm swim down the neck canal and fertilize the egg.
  • Fern gametophyte with young sporophyte x12. The sporophyte grows from a fertilized egg in an archegonium on the gametophyte. The first sporophyte leaf (shown) looks nothing like the large compound leaves produced later by the sporophyte.
  • Angiopteris evecta x30. Sorus on the lower surface of a leaflet.
  • Cyathia furfuracea sorus on lower surface of leaflet, x30.
  • Hemitelia horrida sorus on lower surface of leaflet, x30.
  • Marattia sorus on lower leaflet surface, x30.
  • Azolla caroliniana x20. This is one of the few heterosporous ferns. It is aquatic. The dark structures are called sporocarps. These are aggregations of megaspores and microspores.
  • Scolecopteris x30. This is a petrified Pennsylvanian-age fossil fern. You can see a cross section of a leaflet (pinnule) with sporangia underneath. The specimen is from a southern Illinois coal mine.
  • Botryopteris petiole xs x20. This is a petrified Pennsylvanian-age fossil fern from eastern Kentucky.

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