[R] font size in the trellis plot

[ronggui]

>library(lattice)
>dotplot(variety ~ yield | site, data = barley, groups = year,
             key = simpleKey(levels(barley$year), space = "right"),
             xlab = "Barley Yield (bushels/acre) ",
             aspect=0.5, layout = c(1,6), ylab=NULL)

and i get the plot whose font overlaps .what parematers should i change.(i do not want to change the size of the plot).