What happens to the prothallus as the embryo transforms into the sporophyte?

As the embryo develops into the sporophyte, the prothallus, which is the gametophyte stage of ferns, begins to degenerate. The sporophyte, which is the diploid generation, relies on the prothallus for initial nutrients and support before it becomes independent. Eventually, the prothallus will die off as the mature sporophyte establishes itself and starts to photosynthesize and grow on its own. Thus, the prothallus serves a temporary role in the life cycle of ferns.