As you're venturing through one of the more densely wooded patches of Central Park — say, in the West Seventies — you come to a clearing and are confronted by an apparition: two beautiful women in exotic finery (very little of it in one case) kneel before a floating spirit. Transfixed, you watch the séance, trying your best to stay hidden — until … So goes only one of the countless possible fairy tales that can unspool after looking at the watercolor-on-canvas paintings of Brooklyn-based Bettina Sellmann. See this particular reverie-inducer at Derek Eller Gallery through August 15. —Andrew M. Goldstein