Three series of cross-fractionated branched polyethylenes having molecular weights in the ranges 20 000, 60 000 and 110 000 and branch contents ranging from zero to 32 hexyl branches per 1000 C atoms have been studied. Both linear and bulk growth rates have been determined using optical methods. The two lower molecular weight groups show a regime I-regime II transition, which translates to lower temperatures as branching is increased. The highest molecular weight series shows either a regime II-regime III transition or simply regime III. The transition temperature also translates to lower temperatures as branching increases. The rate of secondary nucleation is reduced by branching, but the rate of reptation is reduced by increasing molecular weight causing the aforementioned effects. It is suggested that the appearance of the regime II-regime III transition is caused by a change in nucleation mechanism.