The art of growing plants in containers is ancient, nearly as old as the invention of pottery itself. At first, growing in containers was most likely practical in nature, but certain cultures -- Egypt, China, Japan, Korea, Vietnam, Thailand -- began to develop the practice for aesthetic reasons.
Bonsai as an art form usually centers around the practice of growing trees in miniture form, using in shallow containers and maintained with tools to fashion and maintain the plant as a miniture form of itself. The goal for growing trees as Bonsai plants is to train the tree to look old, but if grown correctly, the plants can, indeed, grow to be quite old, lasting for generations. In fact, the oldest known Bonsai tree is a pine that is soon to be 500 years old!
Bonsai pots are most notible for their shallow depth. They can be used for growing other types of minitures besides trees. The cactus in this picture is just a sprout, but its shallow root system will allow a shallow container. It will be interesting to see if the shallow depth of the container will inhibit the growth of the cactus over time.
Rather than start from seed, many Bonsai enthusiasts look for small nursery stock for starter plants. This way one can choose plants that show characteristics that suggest the desired shape and age. Dry Creek carries several types of miniture trees.