This lesson is based on the National Register of Historic Places registration file for the Arnold Arboretum (Massachusetts) and other source material about the Arboretum and Frederick Law Olmstead. The lesson focuses on the first arboretum in the United States, which was part of Olmstead's plan for Boston's park system, known as the "Emerald Necklace." The lesson can be used in teaching units on late 19th-century urban expansion, especially as influenced by immigration and the Industrial Revolution. It also can form the core of an interdisciplinary unit when used in conjunction with lessons on the Romantic and Transcendentalist movements and lessons on botany. The teacher's part of the lesson provides general information, gives educational objectives for students, discusses visiting the site, and lists supplementary resources. The student part of the lesson includes: "Getting Started"; "Photograph Analysis Worksheet"; "Setting the Stage"; "Locating the Site" (Map: Plan of Boston Park System); "Determining the Facts" (Readings: The Establishment of Arnold Arboretum; Olmstead's Views on Parks; Arnold Arboretum Becomes a Reality); "Visual Evidence" (Drawing: Bird's-eye View of Arnold Arboretum; Photos: Construction near Main Entrance, c. 1892; Kalmia in Bloom, c.1900); and "Putting It All Together" (Activities: Being a Plant Explorer, Park Rules and Regulations, Researching a Local Park). (BT)