Observations have been made on rates of increase in total number of cells and on rates of division in isolated pea roots grown in sterile conditions in one series over a period of 9 days and in another started from tips of different lengths. It is shown that when cultures are started from tips of 6.0 mm. excised from germinated seeds the rate of increase in cell numbers increases with time until the fifth day and then decreases to the ninth day. It is further shown that when cultures are started from tips of 3.0, 6.0, and 10.0 mm., the initial lag phase is longer, the peak rate in division occurs later, and the peak value tends to be greater the shorter the initial tip. These observations are taken to indicate that division in the meristem depends partly on the synthesis of appropriate metabolites in the meristem and partly on a supply of metabolites from mature regions of the root.