transparency in segments()

Dear all,
i would like to plot each value from my datasets as segment with defined
transparency
However, I didnt find out how to set the transparency.
definition by "col=" in par() or segments() doesnt seem to work
any suggestions?

example code:
xx2 <-read.table("http://www.scandinavia.sk/data/R/0_05.csv", sep=";",
header=T)
plot(xx2$MEAN_PERI,ylim=c(50,350),xlim=c(1,30000),log= "x",
yaxt='n',ylab="",xlab="mean", type = "n")
segments(xx2$MEAN_PERI, 60,xx2$MEAN_PERI, 100, tcl=-.2)
xx3 <-read.table("http://www.scandinavia.sk/data/R/0_10.csv", sep=";",
header=T)
segments(xx3$MEAN_PERI, 120,xx3$MEAN_PERI, 160, tcl=-.2)
xx4 <-read.table("http://www.scandinavia.sk/data/R/0_15.csv", sep=";",
header=T)
segments(xx4$MEAN_PERI, 180,xx4$MEAN_PERI, 220, tcl=-.2)
xx5 <-read.table("http://www.scandinavia.sk/data/R/0_20.csv", sep=";",
header=T)
segments(xx5$MEAN_PERI, 240,xx5$MEAN_PERI, 280, tcl=-.2)
xx6 <-read.table("http://www.scandinavia.sk/data/R/0_25.csv", sep=";",
header=T)
segments(xx6$MEAN_PERI, 300,xx6$MEAN_PERI, 340, tcl=-.2)

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