Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): Shown is a Saccharomyces cerevisiae colony from which eight stalk-like structures emerge. These multicellular structures are obtained when a dense layer of cells is spread on a plate supplemented with a high agar concentration and later irradiated with UV light. Some of the surviving colonies produce stalk-like structures. In some cases several stalks originate from a single colony. While the average height of the stalks is 0.5 to 1.0 cm, some reach a height of 2.0 cm. These structures are spatially organized and show some degree of cell specialization. (Photo courtesy of David Darom, Hebrew University of Jerusalem, Jerusalem, Israel.) (See related article on page 5402.)