A growth model, introduced to describe the development of branched polymers
in an heterogeneous environment, gives rise to clusters whose boundary is
either faceted or rough. We study the transition between these two morpholo
gies as a function of the parameters of the model. The phase diagram is obt
ained by direct numerical simulations. The nature of the transition is disc
ussed. (C) 1999 Elsevier Science B.V. All rights reserved.