Studies of the Populus tremuloides root system by Day (1944), Sandberg (1951) and Barnes (1959) have all shown lateral roots extending as much as 30 feet from tree base. These roots may branch extensively and sometimes exhibit an "undulating" growth habit. According to the above authors, suckers occur on the segments of these lateral roots which are closest to the soil surface. The objective of this investigation was to quantitatively determine root depth and diameter at the point where suckering occurs. Both trembling aspen (P. tremuloides) and bigtooth aspen (P. grandidentata) were studied.