The purpose of plate counting is to estimate the number of cells present based on their ability to give rise to colonies under specific conditions of nutrient medium, temperature and time. Theoretically, one viable cell can give rise to a colony through replication. However, solitary cells are the exception in nature, and most likely the progenitor of the colony was a mass of cells deposited together.[citation needed] In addition, many bacteria grow in chains (e.g. Streptococcus) or clumps (e.g., Staphylococcus).