  We study numerically the effect of varying the equation of state (EOS) on the
formation of stellar clusters in turbulent molecular clouds. Our results show
that the EOS plays an important role in the fragmentation of the clouds, and
the determination of the initial mass function (IMF) of the protostellar cores.
Fragmentation decreases with increasing adiabatic index $\gamma$ in the range
$0.2 < \gamma < 1.4$, although the total amount of mass accreted appears to
remain roughly constant through that range, resulting in more massive cores at
higher $\gamma$. Fragmentation and collapse ceases entirely for $\gamma > 1.4$
as expected from analytic arguments. Primordial gas may have effective $\gamma
> 1$, in which case these results may help explain why models of the formation
of the first stars produce isolated, massive objects.
