par(mfrow=c(1,2),mar=c(4,3.1,0,0))

attach(ntukey)
mplot(unfactor(lat),y,group=geno,type="b",xlab="(a) latitude by geno",ylab="",
	xaxt="n")
axis(1,as.numeric(levels(lat)),levels(lat))
mplot(unfactor(geno),y,group=lat,type="b",xlab="(b) geno by latitude",ylab="",
	xaxt="n")
axis(1,1:3,levels(geno))
mtext("height",2,2)
detach()

par(tmpar)