  New photometry and spectroscopy for the two rich clusters Abell 665 and Abell
2218 are presented and used to establish the Fundamental Plane (FP) for the
clusters. The FP for these two clusters adds important knowledge about the
properties of E and S0 galaxies in the relatively unexplored redshift interval
0.05 to 0.3. We have compared the FP for A665 and A2218 with the FP for the
three clusters CL0024+16, CL1358+62 and MS2053-04 with redshifts between 0.33
and 0.58, and with the FP for the Coma cluster. The scatter around the FP is
similar for all six clusters. We find that the slope of the FP for the
intermediate redshift clusters is slightly different from the one found for the
Coma cluster and other nearby clusters. This may either be caused by selection
effects for the intermediate redshift clusters or by differences in the
evolution of low luminosity galaxies and high luminosity galaxies. The
mass-to-light (M/L) ratios, as measured from the FP, change with redshift.
Using the data for all five intermediate redshift clusters, we find that the
M/L ratios for photometry calibrated to Gunn r change with redshift as Delta
log M/L_r = (-0.26+-0.06) Delta z for q0=0.5. This is consistent with the
previously published analysis for CL0024+16, CL1358+62 and MS2053-04. For
q0=0.5 the results are consistent with passive evolution of a stellar
population which formed at a redshift larger than five. For q0=0.15 the
formation redshift must be larger than 1.7. Our new data for A665 and A2218
confirm the gradual and slow evolution of the bright E and S0 galaxies.
However, possible star formation in E and S0 galaxies during the last 3-4 Gyr
of the history of the Universe, as well as the selection effects complicate the
interpretation of the data.
