There are five kinds of Challenge classes: multiple stems of multiple varieties of the same class; multiple stems of one variety; multiple stems of multiple classes; bloom progression (3 stems: bud, exhibition bloom, and open bloom with stamens showing); and English-style box (6 roses). Other popular Challenge classes include Most Fragrant, Rose in a Photo Frame, Rose in a Bowl, and Artist's Palette (5 roses, different colors). The Arrangements division consists of floral arrangements in which roses predominate. The ARS offers a series of named Challenge classes, ranging in size from a single Grandiflora in an "appropriate" container, to 5 Old Garden roses in separate containers, to 6 All-American Rose Selection winners in separate containers, to 12 Miniature roses in a clear container. Rose shows using ARS guidelines and standards are judged by ARS-accredited judges working in teams of three. Accreditation requires experience exhibiting, working as a show clerk, attending a judging school, and passing an exam and an apprenticeship. Judging schools in the US are held by the ARS Districts and are required to use the ARS-published Guidelines for Judging Roses as the text. The exam is a standardized national exam. Judges are required to audit the judging school every three years. The ARS has established standard certificates for awards at local society rose shows, for instance Queen, King, Princess; Classic Shrub, Modern Shrub. Local societies are free to use any or all of these certificates, plus other categories as desired. Various publications are used by exhibitors to enter their roses in the right show category. The ARS publishes the Handbook for Selecting Roses, mailed to members annually, which lists most roses in commerce in North America and gives the official Exhibition Name, color class, petal count, year of introduction, and classification. The Combined Rose List is published annually and is used by exhibitors and judges as a reference for official cultivar names and unofficial synonyms, color category and classification, and year of introduction. It includes all roses known to be in commerce worldwide. The Guidelines for Judging Roses is published by the ARS and gives the standards by which roses are to be judged: Form, Color, Substance, Stem and Foliage, Balance and Proportion, and Size. Rose flowers come in different forms. Flowers may be cupped, globular, flat, imbricated (like a camellia) or high-centered. Exhibition flower form is defined by the ARS as a high-centered flower with a circular outline and petals that spiral outwards from the center in a symmetrical manner.