The linear and quasi-linear theory of perturbations in finite-&bgr;, collisionless plasmas that incorporate a sheared velocity flow is developed. A simple, one-dimensional magnetic field geometry is assumed to adequately represent solar wind conditions near the sun, i.e., at R=0.3 AU. Two modes are examined in detail: an ion-acoustic mode (finite-&bgr; stabilized) and a compressional Alfv¿n mode (finite-&bgr; threshold high-&bgr; stabilization). The role played by equilibrium temperature anisotropies, in the linear stability of these modes, is also presented. From the quasi-linear theory, the effects of waves on the state of temperature component (parallel and perpendicular to the magnetic field) of the solar wind is determined: qualitative agreement with the observed anisotropies of electrons and ions is obtained. The quasi-linear temperature changes are also shown to result in saturation of these instabilities.