  We introduce an extended Smoluchowski equation describing coagulation
processes for which clusters of mass s grow between collisions with
$ds/dt=As^\beta$. A physical example, dropwise condensation is provided, and
its collision kernel K is derived. In the general case, the gelation criterion
is determined. Exact solutions are found and scaling solutions are
investigated. Finally we show how these results apply to nucleation of discs on
a plane
