A series of cross-fractionated branched polyethylenes of M(w) about 18 000 and branch contents from zero to 22 branches/1000 carbons have been studied. Both linear growth rates and bulk growth rates have been determined using optical methods. It is demonstrated that increased branching causes the regime I-regime II transition to translate to lower temperatures. This occurs through a greater reduction of the rate of secondary nucleation relative to the reduction that occurs in the rate of surface spreading. Bulk kinetic data can be used to define regimes in polyethylenes to within a few degrees but cannot be used to estimate rates of secondary nucleation and surface spreading or to determine fold surface free energies.