  A comparison of star formation properties as a function of environment is
made from the spectra of identically selected cluster and field galaxies in the
CNOC 1 redshift survey of over 2000 galaxies in the fields of fifteen X-ray
luminous clusters at 0.18<z<0.55. The ratio of bulge luminosity to total galaxy
luminosity (B/T) is computed for galaxies in this sample, and this measure of
morphology is compared with the galaxy star formation rate as determined from
the [OII]3727 emission line. The mean star formation rate of cluster galaxies
brighter than M_r= -17.5 + 5 log h is found to vary from 0.17 +- 0.02 h^{-2}
M_sun/yr at R200 (1.5-2 Mpc/h) to zero in the cluster center, and is always
less than the mean star formation rate of field galaxies, which is 0.39 +- 0.01
h^{-2}M_sun/yr. It is demonstrated that this significant difference is not due
exclusively to the difference in morphological type, as parameterized by the
B/T value, by correcting for the B/T-radius relation. The distribution of [OII]
equivalent widths among cluster galaxies is skewed toward lower values relative
to the distribution for field galaxies of comparable physical size, B/T and
redshift, with a statistical significance of more than 99%. The cluster
environment affects not only the morphological mix of the galaxy population,
but also suppresses the star formation rate within those galaxies, relative to
morphologically similar galaxies in the field.
