using dimnames as main when plotting with lapply

Dear all,



# 1. I use tapply to calculate various things based on a grouping variable.

# simple example using the warpbreaks dataset:
tmp <- with(warpbreaks, tapply(breaks, tension, range))
tmp
dimnames(tmp)

# 2. I wish to plot the result of each element of tmp, using the names
of the elements in tmp as 'main' in each plot

# My attempt:
# par(mfrow = c(3, 1)) # my preferred 'par' in this case.
lapply(tmp, function(x) plot(x, main = dimnames(x)))

Apparently not the right way to extract dimnames to main. Any suggestion
of how to proceed?

Thanks in advance for any comments.

Henrik