bubble plot in R

Motived by the post from FlowingData(http://flowingdata.com/2010/11/23/how-to-make-bubble-charts/), I made this plot with R code below:

par(mfrow=c(3,1), mar=c(4,6,4,4))
for(ty in c("protein_coding","lincRNA","piRNA")){
             res1=subset(res,type==ty & readsCount>10 & speciesCount>8)
             symbols(log(res1$length), res1$speciesCount, circles=sqrt(res1$readsCount/ pi ), inches=0.35, fg="white", bg="red", cex.lab=2, cex.main=2, cex.axis=2, xlab="intron size (log(bp))", ylab="species count", main=ty, xlim=range(log(res$length)))            
}

I will continue to adapt code for legend from this article (http://www.jstatsoft.org/v15/i05/paper).