All arguments are optional.
  title specifies title for axis.
  ticks specifies positions of ticks along axis. If None, ticks are
    inferred using sensibleticks. If [], no ticks are drawn.
  labels specifies labels to put by ticks. If None, tick coordinates
    are used. If [], no labels are drawn.
  y specifies intersect with y-axis. If None, defaults to a reasonable
    position below the data. (Default is 0.)
  lim specifies left and right edges as a tuple or list. If None,
    lim is determined from ticks. If [], no line is drawn.
  flip, if True, inverts the sign of the settings from ticklen, textdist,
    and axshift.
Either ticks or labels (but not both) may be a function, in which case the labels are calculated from the tick positions (or vice versa). For example:

  xaxis(0, lambda x: x/100, np.arange(0,101,25), 'value (%)')

Without any arguments or with just a title as an argument, xaxis tries to determine sensible defaults based on previous calls to plot and friends. Your mileage may vary.