Height growth in hemlock (Tsuga canadensis (L.) Carr., T. heterophylla (Raf.) Sarg., T. mertensiana (Bong.) Carr.) is by rhythmic growth of a monopodial axis with continuous branch production throughout the growing season. Leader growth is plagiotropic and leader erection is a process lasting several years. Two types of events disrupt the basically monopodial nature of the axis. (1) Frequent (43%) apical meristem death shifts dominance to a nearby lateral branch in T. canadensis. (2) Weak apical control allows occasional shifts in dominance from the leader to a branch without meristem death (13 and 24% in T. heterophylla and T. canadensis, respectively, but none in T. mertensiana). These growth patterns contain elements of several tree architectural models but fit none well.