[R] multiple lines on multiple plots

[James Annan]

I'm sure this must be trivial, but I'm a novice with R and can't work 
out how to handle the axes when I am constructing multiple plots on a 
page and try to return to a previous one to put multiple data sets it.

A simple example:
---
x<- 1:10
y<- (1:100)*3
par(mfcol=c(2,1))
plot(x)
plot(y)

par(mfg=c(1,1))
lines(x)
---

The first 5 lines make two plots with a row of dots along the diagonal 
of each. I intended the last two statements to add a line to the first 
plot, that runs along the same data points already plotted there. 
However, although the commands add a line to the top plot, it is clearly 
using the axis dimensions of the lower plot. Can someone tell me how to 
get it to use the axes that are already there?

Variants like lines(x,xlim=c(1,10)) have no effect.

Thanks in advance for any help.

James
-- 
James D Annan jdannan at jamstec.go.jp Tel: +81-45-778-5618 (Fax 5707)
Senior Scientist, Research Institute for Global Change, JAMSTEC
(The Institute formerly known as Frontier)
Yokohama Institute for Earth Sciences, 3173-25 Showamachi,
Kanazawa-ku, Yokohama City, Kanagawa, 236-0001 Japan
http://www.jamstec.go.jp/frcgc/research/d5/jdannan/