如何增加R相关图的直方图中标签的大小？

如何解决如何增加R相关图的直方图中标签的大小？

我使用以下已知函数创建R相关图：

# correlation plot #
panel.hist <- function(x)
{
  usr <- par("usr"); on.exit(par(usr))
  par(usr = c(usr[1:2],1.5) )
  h <- hist(x,plot = FALSE)
  breaks <- h$breaks; nB <- length(breaks)
  y <- h$counts; y <- y/max(y)
  rect(breaks[-nB],breaks[-1],y,col="lightgrey")
}


panel.cor <- function(x,digits=2,prefix="",cex.cor)
{
  usr <- par("usr"); on.exit(par(usr))
  par(usr = c(0,1,1))
  r <- cor(x,use = "pairwise.complete.obs")
  txt <- format(c(r,0.123456789),digits=digits)[1]
  txt <- paste(prefix,txt,sep="")
  if(missing(cex.cor)) cex <- 0.8/strwidth(txt)
  
  test <- cor.test(x,y)
  # borrowed from printCoefmat
  Signif <- symnum(test$p.value,corr = FALSE,na = FALSE,cutpoints = c(0,0.001,0.01,0.05,0.1,1),symbols = c("***","**","*","."," "))
  
  text(0.5,0.5,cex=2)
  text(0.8,0.8,Signif,col=2,cex=2)
}


pairs(USJudgeratings[,c(2:3,6,7)],lower.panel=panel.smooth,upper.panel=panel.cor,diag.panel=panel.hist)

现在，我想增加变量名的直方图标签的字体大小（标签用黑框标记）。该怎么办？