newbie question: xterm display for plot()

[Don Roberts]

    Hi;
    I'm running Octave under YDL on a PS3.  A few months ago I was able to =
    access it and run plots fine by ssh from my iMac.  Executing a plot() =
    poped open a new Xterm on the Mac and displayed the plot just fine.  Now =
    when I open an xterm on the Mac and ssh into the PS3 (ssh -x -l ...) I =
    can still run Octave just fine, put plot() results in=20
            unable to open display '  '
    I'm not sure if this is properly an Octave, Xterm, PS3, YDL, or Mac =
    question so I'm hoping someone can at least point me in the right =
    direction.  What step(s) have I forgotten?
    thanx,
    Don Roberts