  The spreading of liquid drops on surfaces corrugated with micron-scale
parallel grooves is studied both experimentally and numerically. Because of the
surface patterning, the typical final drop shape is no longer spherical. The
elongation direction can be either parallel or perpendicular to the direction
of the grooves, depending on the initial drop conditions. We interpret this
result as a consequence of both the anisotropy of the contact line movement
over the surface and the difference in the motion of the advancing and receding
contact lines. Parallel to the grooves, we find little hysteresis due to the
surface patterning and that the average contact angle approximately conforms to
Wenzel's law as long as the drop radius is much larger than the typical length
scale of the grooves. Perpendicular to the grooves, the contact line can be
pinned at the edges of the ridges leading to large contact angle hysteresis.
