An 8- by 16-foot scale model of Harvard's Arnold Arboretum, with more than 4,000 miniature trees, is the centerpiece of a new permanent exhibit there entitled "Science in the Pleasure Ground." Located in the Hunnewell Building, the exhibit is free and open to the public. Arboretum director Robert Cook says the new exhibit, which cost $300,000 to produce, will give visitors an appreciation for the breadth and complexity of the landscape. "The Arboretum is not a park," says Cook, "but a collection with an educational mission." The model relates surrounding exhibits on the design of the Arboretum's landscape, historic plant collecting expeditions, and work in forest conservation to specific locations on the grounds. Other exhibits focus on the evolution of the American residential landscape, and on the uses of wood in the early industrialization of America.