A colony is population of a single type of microorganism that is growing on a solid or semi-solid surface. Bacteria, yeast, fungi, and molds are capable of forming colonies. Indeed, when a surface is available, these microbes prefer the colonial mode of growth rather than remaining in solution.

On a colonized solid surface, such as the various growth media used to culture microorganisms, each colony arises from a single microorganism. The cell that initially adheres to the surface divides to form a daughter cell. Both cells subsequently undergo another round of growth and division. This cycle is continually repeated. After sufficient time, the result is millions of cells piled up in close association with each other. This pile, now large enough to be easily visible to the unaided eye, represents a colony.

The appearance of a colony is governed by the characteristic...