tmpar <- par(bty="n",yaxt="n",mar=c(2.1,0.1,0.1,0.1),mfrow=c(3,1))

plottwo <- function(trt, con, A = "T", B = "C",xlim=c(0,500), xlab="", ...)
{
	ry <- range(c(trt$y, con$y))
        plot(range(c(trt$x, con$x)), ry, type = "n",
	   xlim=xlim, xaxt="n", xlab="", ...)
	text(xlim[1],ry[2]*3/4,xlab,adj=0,cex=1)
        lines(trt)
        lines(con)
        text(mean(trt$x), max(trt$y)/2, "T",cex=1)
        text(mean(con$x), max(con$y)/2, "C",cex=1)
}
normden <- function(mean=0,sd=1,n=100,x=mean+3*sd*(-1+(0:100)*.02))
{
        list(x=x,y=dnorm(x,mean,sd))
}
plottwo(normden(200,30),normden(300,30),
	xlab="(a) equal variance",ylab="")
axis(1,seq(0,500,by=100),lab=F)
plottwo(normden(200,20),normden(300,45),
	xlab="(b) variance increases\nwith mean",ylab="")
axis(1,seq(0,500,by=100),lab=F)
plottwo(normden(200,45),normden(300,20),
	xlab="(c) variance to mean tradeoff",ylab="")
axis(1,seq(0,500,by=100),cex=.7)
par(tmpar)

rm(plottwo,normden,tmpar)