One of the primary advances of ferns over bryophytes is the development of a vascular system. This, consisting of tissue named xylem and phloem allows water to be transported from the roots, where it is absorbed, to all the other cells in the plant's body.
In bryophytes, water is absorbed by structures called rhizoids and spread throughout the plant's body by the process of diffusion. This is limited to a few centimeters.
With the presence of the vascular system ferns are capable of growing larger, and their habitat has also widened compared to bryophytes.