How to change label size in a plot

Dear all,

I have created a plot like this:

matrix<-read.table("G:\\my documents\\names.txt",header=T)
hc<-hclust(dist(matrix)^2,"cen")
memb<-cutree(hc,k=10)
plot(hc,col="black")

This prints out a dendrogram with labels, but the text of the labels is
large, so they overlap and are unreadable. How can I decrease the size of
the lable text on a dendrogram so that it does not overlap and is therefore
readable?

I know the question is similar to that posted by Michael Schmitt on 19 March
2005, but as far as I can see, the question was not answered.

Many Thanks,

Fiona