WASHINGTON ??" The Smithsonian's annual orchid exhibition is now open in the Arts and Industries Building through May 26. The array of plants in the show will change constantly, so visitors who come back again and again will discover new treasures in "Nature's Jewels: A Living Exhibit of Orchids and Butterflies." This is the ninth annual exhibition featuring orchids from the collections of the Smithsonian's Horticulture Services Division and U.S. Botanic Garden, but the first time that hundreds of live butterflies in a 1,000-square-foot free-flight enclosure will be included. Visitors will be able to see more than 40 different species of butterflies by walking through the enclosure or looking through the large observation windows. Daily tours at 2 p.m. will give visitors a chance to learn about orchids, which appear on every continent (except Antarctica) and have adapted to almost every environment on the globe. For a detailed schedule of events, visit www.smithsonian.org/horticulture or call 202-357-2700.