Large clonal differences in sucker production from root cuttings and in rooting of greenwood stem cuttings taken from root suckers were found among nine Wyoming trembling aspen (Populustremuloides Michx.) clones. There appeared to be no correlation between the suckering and rooting capacity of a clone. Formation of callus at the cut ends of sucker cuttings hindered rooting.

The role of carbohydrate reserves in initial sucker growth from excised roots of Alaskan and Utahan aspen (Popnlustremuloides Michx.) was investigated by correlating the seasonal variation in sucker production in darkness with the concentration of total nonstructural carbohydrates (T.N.C.) in the roots. Sucker numbers were not correlated with T.N.C. content. Dry weight of suckers per cutting (D.W./C) was a function of T.N.C. percentage and the number of suckers per cutting (No./C). In the additive model, D.W./C = b0 + b1 (No./C) + b2 (T.N.C), T.N.C. was a significant contributor to sucker dry weight. Although dry weight per cutting increased as the number of suckers became larger, dry weight per sucker decreased. Within geographic area, number and dry weight of suckers and T.N.C. percentage were related to both date of collection and clone of origin. Seasonal trends in T.N.C. content were similar in the Utahan and Alaskan roots studied.

Differences in suckering from root segments and in rooting from sucker cuttings were studied among four species of Populus, including three poplars, P. angustifolia James, P. deltoides Bartr., and P. balsamifera L., and an aspen, P. tremuloides Michx. Places where suckers originated on root segments were more variable in the poplars than in the aspen. Whereas suckers developed in the aspen only from the periderm, suckers developed in the poplars from the periderm and from cambium exposed at the cut ends of segments and lateral roots. Poplar suckers arising from the periderm originated from preexisting suppressed buds embedded in the periderm. Suckers developed in the aspen from preexisting primordia. Lateral root formation from preexisting and newly initiated meristems on root segments was common in the poplars but rare in the aspen. The presence of lateral roots increased sucker growth, and the development of suckers and lateral roots responded to the inherent polarity of the root segment. Sucker cuttings from the poplars were generally superior in rooting capacity to those from the aspen.

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Seasonal variation in number of suckers produced from root cuttings of three clones of trembling aspen (Populustremuloides Michx.) was related, in a negative manner, to the quantity of endogenous auxin in the roots when collected. The mean number of suckers per cutting varied with the clone of origin and time of collection.