Control of X-axis in bwplot

["Robert Platt" <robert.platt@mcgill.ca>]

Hi,

This is probably a simple question, but here goes:

I am using bwplot(y~x|z) to get a set of boxplots of x stratified by y, with 
separate panels for different values of z.  I would
like to control the tick-marks on the x-axis of each panel.

I used

bwplot(y~x|z,scales=(list(tick.number=7))

but it doesn't necessarily give me exactly seven ticks, and they are not 
necessarily where I want them to be.  My x values range
from 0 to 180, and I would like ticks at 30 day intervals.

Does anyone have advice?  I'm looking for something like the "axis" command 
that you can use with non-trellis plots.  I apologize if
this is easy but I am new to trellis graphics.

Robert Platt