  We obtain the NaI 8183,8195 absorption line radial velocity curves for the
polars ST LMi and MR Ser, from which we find the semi-amplitudes to be
K_abs=329=+/-6 kms-1 and K_abs=289+/-9 kms-1 respectively. We find that for
both systems the effects on the \NaI absorption lines due to X-rays heating the
inner face of the secondary are negligible, and so the values obtained for
K_abs can be taken as the true semi-amplitude of the secondary star. We then
determine the projected rotational velocities, vsini, to be 104+/-9 kms-1 and
66+/-13 kms-1 for ST LMi and MR Ser respectively which enables their mass
ratios to be calculated. For ST LMi and MR Ser we find the mass ratio to be
0.22+/-0.04 and 0.10+/-0.05 respectively; values which are significantly
different only at the 94 percent level. We show that ``spike'' in the orbital
period distribution of polars is a significant feature, although the discovery
of only one more system with a period outside the ``spike'' would decrease its
significance below a 99 percent confidence level. We conclude that, even if the
limb darkening coefficients for the secondary stars in ST LMi and MR Ser are
the same, we cannot rule out the two systems having identical parameters.
Therefore our observations are compatible with the theory explaining the
``spike'' in the period distribution of the AM Hers.
