Fern prothallus is developed from

Step-by-step solution

In ferns, spores germinate to form a prothallus. Ferns are known as homosporous plants. The sporangia are usually in clusters known as sori, found on the underside of the fern leaves. Some ferns have a covering over the sporangia known as an indusium. When the spores are mature, they are released from the sporangia. If a spore lands on a suitable site, it will germinate and grow via mitosis into a mature gametophyte plant (prothallus). A gametophyte is a plant that produces gametes.