"plot"(x, xylim="auto",clab=1:nrow(X),lab.cex=1,lab.col="black",...)xylim[1,1], xylim[1,2]) of the plot.
The y limits (xylim[2,1], xylim[2,2]) of the plot.
Note that xylim[i,1] > xylim[i,2] (i=1, 2) is allowed and leads to a 'reversed axis'.