DEVOTEES, here’s the hot new thing: “Go forth and multiply.” Runners, offsets, and suckers become respectable in Root, Nurture, Grow: The Essential Guide to Propagating and Sharing Houseplants (Caro Langton and Rose Ray, Quadrille Press, $24.99). Not only are houseplants fun and pretty, but they are good for you as well, helping purify the air and bringing a bit of the peaceful green world to your living space. Exquisitely photographed, with clear, concise instructions, the renowned designers of Ro Co take you step by affordable step through the magical process of creating more plants. Master the art of division, grafting, and air layering with style. Cultivating, pruning, and tending are all nicely presented in this crisp volume. Look inside for lots of DIY projects, as well, including making root chutes and grow packets. You will be the star of the plant swap, with loads to share.