[R] troubles with displaying legend on the plot

[Wladimir Eremeev]

Dear colleagues,

I have troubles while trying to display legend on the plot.

I have data.frame fr

> fr
   year  M1             M2
1  1979  58.85198     56.77303
2  1980  57.59725     55.93749
3  1981  57.32133     55.55232
4  1982  54.69320     53.10566
5  1983  56.58973     55.03811
6  1984  58.81363     56.97641
7  1985  58.35583     56.82091
8  1986  60.41842     58.45457
9  1987  58.75928     57.03679
10 1988  59.89553     58.69077
11 1989  51.03595     49.45001
12 1990  52.23915     50.96713
13 1991  46.50311     45.50370
14 1992  47.38811     46.31649
15 1993  48.58066     47.44610
16 1994  46.04452     44.82441
17 1995  46.41809     45.54565
18 1996  37.65783     36.48118
19 1997  60.16313     58.63771
20 1998  51.47550     50.43720
21 1999  52.56228     51.64243
22 2000  41.71746     40.79734
23 2001  44.71175     44.05241
24 2002  49.78033     47.91608

actually I've loaded it from MySQL database.

Now drawing this plot with the following plot.r

===8<====
op<-par(no.readonly=TRUE);

par(usr=c(1979,2002,20,90),mar=c(7, 4, 4, 2) + 0.1);

plot(fr$year,fr$M1
     ,cex=0.8
     ,type="o",ylim=c(20,90),xlim=c(1979,2002)
     ,xlab="year",ylab="M, %"
     ,pch=20
     ,xaxt="n",
     );

lines(fr$year,fr$M2);
points(fr$year,fr$M2,pch=21)
axis(1,at=c(1979:2002));

for(x in 1979:2002) {
  abline(v=x, col = "lightgray", lty = "dotted");
}
for(y in seq(20,90,10)){
  abline(h=y, col = "lightgray", lty = "dotted");
}
legend(1979,0,
       legend=c("M1","M2"),
       pch=c(20,21));

par(op);
===8<===

Legend doesn't appear.
I tried different coordinates, (1979,0), (0,0),
different colors, etc...

Nothing helps. What should I do to make the legend to appear?

I'm using R 1.6.2 for windows.
OS: Windows NT workstation 4.0.

Thank you in advance.
-- 
Best regards
Wladimir Eremeev                                     mailto:wl at eimb.ru

==========================================================================
Research Scientist                                Leninsky Prospect 33,
Space Monitoring & Ecoinformation Systems Sector, Moscow, Russia, 119071,
Institute of Ecology,                             Phone: (095) 135-9972;
Russian Academy of Sciences                       Fax: (095) 954-5534