Fern frond, light micrograph (LM). Transverse section through the frond of a fern (Cyrtomium falcatum), showing the sporangia. At right is a central vascular bundle (meristele) with central xylem tissue (red) surrounded by phloem (light green). On the underside of the frond is a sorus (left) consisting of an umbrella-shaped indusium with a handle-shaped base (placenta), from which protrude numerous stalked sporangia (containing the reproductive spores). A trophophyll frond is a vegetative leaf analogous to the typical green leaves of seed plants that does not produce spores, instead only producing sugars by photosynthesis. A sporophyll frond is a fertile leaf that produces spores borne in sporangia that are usually clustered to form sori. Magnification: x15 when printed at 10 centimetres wide.