During balanced growth of cells in culture all extensive properties of the culture — e.g. cell number, total mass, total DNA content — increase exponentially at the same specific growth rate. Therefore, in some average sense, each component of a cell must double between birth and division. For DNA there exists an elaborate mechanism to ensure precise replication of the genetic material and accurate partitioning of identical copies of the genome to the two daughter cells. Do cells possess another mechanism that intentionally relates the timing of cell division to overall increase in cell size, or is the coordination of growth and division an incidental consequence of size-independent rules for progress through the cell cycle?.