how to set the x-axis of barplot

This has been questioned many times like this one X axis in Barplot in R

however none helped me to solve my problem

dt<- structure(c(79L, 54L, 37L, 41L, 42L, 121L, 134L, 169L, 23L, 19L, 
22L, 19L, 25L), .Names = c("Experi_1", "Experi_2", "Experi_3", 
"Experi_4", "Experi_5", "Experi_6", "Experi_7", "Experi_8", "Experi_9", 
"Experi_10", "Experi_11", "Experi_12", "Experi_13"))

I plot my data like this

mydt<- barplot(dt)

if I do this , it overlay twice the x-axis

axis(side=1,at=mydt[1+c(1,13)],labels=c("Experi1","Experi13"))

It set few of the x-axis labels automatically. I want to do it manually, for example get only mention beginning of x-axis label and end . In this case Experi1 and Experi 13. I tried to understand ?axis and specially label but I could not set it to a costume as axis label as I want.