The cells on the inside also have no way to dispose of the wastes that they once simply pushed out through the cell wall. The need to develop distribution systems had to be met before more complex organisms could develop. As we learned in Important Landmarks in the Evolution of Land Plants, the earliest land plants, such as the mosses, did not have vascular structures. Their cells absorbed moisture and minerals by letting liquids move slowly through their cell walls. This worked for them because mosses are very small plants.
Mosses live in moist environments where water is freely available.
The ferns developed vascular structures. They grew roots so that they could get moisture and minerals from the soil. These roots were hidden in darkness in the ground. They had no way of synthesizing the food that they needed for life and growth. Above the ground, the fronds of the ferns spread out to catch the light.