Observations were made on the seasonal root activity of 2—0 seedlings of red pine (Pinus resinosa Ait.) growing in controlled environments. Portions of the growth pattern conformed closely to the seasonal pattern commonly reported for field environments even though environmental variation was minimized in the controlled experiment. The nature of this pattern was determined by varying temperature, photoperiod, and soil moisture. It was concluded that the gross pattern of root activity is endogenously controlled although environmental variation may induce significant quantitative changes in activity and influence the timing of events.