Fertile fronds taller than the sterile, having from one to five pairs of intermediate pinnæ contracted and bearing sporangia.

On the leaves of this generation arise the sporangia which contain the spores.

Stem simple, two to ten inches high, bearing one smooth, entire leaf about midway, and a terminal spike embracing the sporangia, coherent in two ranks on its edges.

In ferns, an indusium; in filmy ferns, cup-shaped growths encircling the sporangia.

The indusium is formed of the altered margin of the pinnule, at first reflexed to the midrib, giving it a pod-like appearance, but at length opening out flat and exposing the sporangia.