plot order in multi-panel figure

Hi, 

Does anyone know if there is a way to 'reset the plot number' on a 

For instance, I want to have two plots on stacked top of each other (mfrow=c

lines spanning both figures vertically.

split.screen(c(1,1))

screen(1)
plot.window(c(0,1),c(0,1))
abline(v=seq(0,1,by=0.2),lty=3)
split.screen(c(2,1))

screen(2)
plot.new()
plot.window(c(0,1),c(0,1))
for(i in 1:2) axis(i)
box(bty="L")
rect(0.2,0.2,0.5,0.5,col=8)
screen(3)
plot.new()
plot.window(c(0,1),c(0,1))
for( i in 1:2) axis(i)
box(bty="L")
close.screen()