  Perpendicular electron dynamics and the associated collisions are discussed
in relation to the collisional drift wave instability. In addition, the limit
of small parallel wave numbers of this instability is studied and it is shown
to yield a reduced wave frequency. It is also shown that in this case the
growth rate in fact {\em decreases} for smaller parallel wave numbers, instead
of growing proportional to $1/k_z^2$. As a result, the growth rate appears to
be angle dependent and to reach a maximum for some specific direction of
propagation. The explanation for this strange behavior is given. A similar
analysis is performed for acoustic perturbations in plasmas with unmagnetized
ions and magnetized electrons, in the presence of a density gradient.
