X11 error in MAC OS X

When I try to run x11 on my mac in R i get the following error:

x11() Error in .Exteal2(C_X11, d$display, d$width, d$height, d$pointsize, : unable to start device X11 In addition: Waing message: In x11() : unable to open coection to X11 display ''

can someone tell me how to get x11 working? I have OS X version 10.9.5