How to add titles to each plot created from lapply in R?

Question

I am trying to add the variable name (i.e., x, y, and z) as the title for each boxplot:

   bpdf = data.frame(group=c("A","A","A","B","B","B","C","C","C"),
                   x=c(1,1,2,2,3,3,3,4,4),
                   y=c(7,5,2,9,7,6,3,1,2),
                   z=c(4,5,2,9,8,9,7,6,7))

    par(mfrow=c(1,3))
    lapply(bpdf[-1],function(x){
    y <- sort(tapply(x,bpdf$group,median),decreasing=TRUE)
    boxplot(x~factor(bpdf$group,levels=names(y)), 
            main=paste(colnames(bpdf[-1])))
    }) 

I am missing something in the main call (ht to agstudy for previous help).