Well-adapted cells, which had been initiated from root tissue of Ipomoea and of Daucus carota, were grown in 7.5-liter stirred-jar fermenters, and both the cells and media were analyzed for major components at intervals during the growth period. Controlled variables included the size of inoculum, the amount of sucrose, and the source and amount of nitrogen in the media.The data obtained indicate that there are two distinct growth phases in the development of batch cultures of these cell lines. The first, which we term "cytoplasmic growth phase," begins immediately upon addition of inoculum to fresh medium and is characterized by a high rate of nitrogen uptake and metabolism relative to the increase in cell dry weight. The second, or "maturation phase," is characterized by large increments in dry weight and total cell carbohydrate relative to the increments in cell nitrogen. It is suggested that the classical lag, log, and stationary phases of bacterial growth could apply only to the early hours of cytoplasmic growth, if indeed they are relevant at all.