[R] png inside loop

[Sacha Viquerat]

hello list! I'm sorry, I just stumbled over this strange behaviour (at 
least I am not able to explain the behaviour, therefore I assume it to 
be a strange behaviour):

attach(water) # I know, this is not recommended

names(water[3:10])
[1] "temp" "pH"   "DO"   "BOD"  "COD"  "no3"  "no2"  "po4"

for (i in names(water)[3:10]){
     fname<-paste("Henni/GFX/fem",i,".png",sep="")
     mname<-paste("Henni/GFX/mal",i,".png",sep="")
     png(fname,1000,1000)
     xyplot(N_female~eval(parse(text=i)) |group,xlab=i,ylab="Abundance")
     graphics.off()
     png(mname,1000,1000)
     xyplot(N_male~eval(parse(text=i)) |group,xlab=i,ylab="Abundance")
     graphics.off()
}

well, to anyone's surprise, there are no plots in the folder. the loop 
finishes (i, fname and mname have values assigned) and executing

png(fname,1000,1000)
xyplot(N_female~eval(parse(text=i)) |group,xlab=i,ylab="Abundance")
graphics.off()

does produce a png in the folder. I assume this to be caused by the png 
function, since removing the graphics.off() and playing with dev.off() 
and the likes did not help. anyone ideas?? am I missing the obvious??