Plants are placed into two simple kingdom subsections: nonvascular and vascular plants. The big distinction between the two groups is that vascular plants have vascular_tissues: tissues that conduct water and dissolved food in the plant body. The vascular tissues include xylem, which moves water and minerals upward through the plant and phloem, which moves dissolved food downward in the plant.
Nonvascular plants lack these tubes, and therefore must be small and thin so that each cell can acquire its needed materials via passive_transport from the plant's surface, or from other cells within the plant that are located near the surface.
Regardless of whether a plant is vascular or nonvascular, it has structures that (1) anchor it into the soil, (2) provide physical support for its photosynthetic structures, and (3) specialize in performing photosynthesis.
The difference is that in nonvascular plants these structures are called root-like, stem-like, and leaf-like because they lack vascular tissues. True roots, stems, and leaves are those body structures that contain vascular tissues.
Highly developed vascular systems allow the production of an effective adult plant body, with sufficient reserves to allow the investment in specialized body structures used for reproduction. Good vascularization also provides for structures used to enhance dispersal of the gametes and/or fertilized eggs.
Ferns are vascular plants, but they are seedless. The gametophyte is a brief and physically small stage in the life cycle of a fern. The dominant stage is the asexual sporophyte stage that we call the fern frond.
When the average person thinks of ferns, they think of the fronds. Most people have never even seen the tiny gametophytes. Each gametophyte bears the developing archegonia (female structures) and antheridia (male structures) that will develop and release spores. Rhizoids are present to anchor the gametophytes in the soil.
A sorus (sori) is a cluster of several sporangia. Photo Atlas micrograph 52B shows the surface of a fern leave (frond), which is called the pinna. Scattered around the pinna are multiple sporangia in tight clusters (sori). Our microslide will look more like micrograph 52D, which is a cross-section of a sorus that is still embedded in the frond. The indusium is a protective epidermal membrane that covers sori.