[R] negative values for barchart

[Plantky]

Hi all,

My data has some positive and negative values, and I want to plot a
barchart. The problem is that the y-axis zero is somewhere in the
middle of the plot, and the graph starts with a negative value. How
can I make the negative values appear as bars that are going below the
y-axis zero?
So the desired graph would have some bars projecting up and some down.

Thanks.
Plantky