Next time you're on the A40, spare a thought for Oxford's horticultural development officer, John Alcock, who told the Times last week about the intricacies of roundabout design.'The roundabouts are always a challenge, ' he declares. 'The perfect flowers are geraniums, petunias and marigolds, all of which can tolerate fumes, ' he says, 'though you can get a bit bored with marigolds. On the Woodstock roundabout we've six beds with horseshoe shapes, and I'm very proud of them. We have star shapes and pizza quarters on Rosehill. I steer clear of animal shapes because they might attract a driver's eye too much.'