Photomicrograph showing a vertical section of sorus of a fern X60

Information about the sori:

1. Sori are spore-producing structures on the undersurface of the fronds of fern. They are visible as rows of small brown dots.

2. Sori (groups of spore-producing reproductive structures) are the plural of sorus.

3. In some ferns, the sorus consists of an indusium which is the kidney-shaped covering of the sorus. Indusium protects the developing sporangia but it withers when the sorus ripens to expose the sporangia.

4. Sori are present in the sporophyte of fern. They are responsible for spore formation. The spores will give rise to gametophyte.

5. There are many sporangia - the spore casings that hold the spores in a sorus. The sporangia are usually tiny - maybe half a millimetre (one fiftieth of an inch) across. Each sporangium has an annulus. This structure helps to disperse the spores when the weather suddenly becomes dry.