  We compare the evolution of morphology in X-ray cluster data and in clusters
obtained in a simulation of flat CDM, normalized to the observed cluster
abundance. We find that the evolution rate in model clusters is significantly
higher than in data clusters. The results is stricking, as our cluster data are
all just for $z \simlt 0.2$, but is not contrary to expectations, as is known
that the CDM spectrum is too flat, around the cluster scale, and therefore
induces the presence of too many substructures. The cluster simulations were
run using a TREESPH code and therefore include hydrodynamical effects. The test
we performed, which turns out to be very sensitive, starts from the so--called
power ratios introduced by Buote and Tsai, and makes use of the 2--dimensional
generalization of the Kolmogorov--Smirnov test. The discrepancy between data
and model is however directly visible through linear regression techniques and
using simpler statistical tests.
