Rhododendrons, azaleas, mountain laurel and andromeda thrive in the cool, moist atmosphere of a narrow protected valley that lies just east of the Highland Reservoir. A modest but popular display in 1900, the Rhododendron Collection was significantly expanded by former Superintendent of Horticulture Richard A. Fenicchia. Today, this dell features nearly 700 specimens representing 175 species, varieties or forms, at its best in late May and June, when shrubs are ablaze with brilliant red, pink, orange, yellow and white blossoms.