Note the curled tips of the fronds. These have uncurled almost all the way. The sori on the leaves of this type of fern are shown below. This photo shows the underside of a fern leaf, enlarged so you can see the sori. This photo shows a slice through a sorus on a fern leaf, as seen through a microscope.
B falls off when the spores are ready for release.
You can see more than a dozen sporangia in this photo, each containing spores. Each spore is a single cell that is capable of dividing if it lands in a moist, protected spot. By cell division, it grows into the prothallium shown below. It is tiny and fragile, only about 1-3 millimeters across. It is visible with the naked eye, but a microscope is required to see the sex organs on its surface.