In some plants like monocotyledonous (corn and rice) the primary root is short lived and is replaced by a large number of fine roots of similar diameter. These roots originate from the base of the stem and constitute the fibrous root system.
Adventitious roots do not develop from another root.
In some plants, like GRASS, MONSTERA and BANYAN TREE, many roots arise from parts of the plant (from a stem, leaf or other plant parts) other than the radicle. These types of roots are called adventitious roots.