Wikipedia tells there are several different types of roots. They suggest a root is an organ of a plant that grows no leaves, and usually resides underground. Their purpose of course, include: a) absorption of water and inorganic nutrients, b) structural support, c) storage of food and nutrients, and d) vegetative reproduction.
We recently had a Foxtail Palm installed and were advised not to cover roots near the surface because these are aerating roots. These have breathing pores for the exchange of gases.
Stunted pot plants cannot reach full potential tells that roots can determine the size of the pot and restricts the growth of the plant. What is puzzling is that the plants do not attempt to grow the roots in a ball and occupy the volume of the pot. Instead, the roots seek the edge of the pot and apparently send a signal to say, 'stop growing'. This 'signal' is cytokinin, which is similar to an animal's hormones, which provide communication throughout the body of the plant.
Researchers discovered that doubling a pot's size permitted the plant to grow almost 50 percent larger.