1. Boil juice in small saucepan until reduced to 2/3 cup. Whirl together juice and vinegar in blender. With blender on, slowly pour in oil; blend until thoroughly incorporated. Blend in salt and pepper.Salad:
2. Combine watercress, half the orange segments and half the onion rings in large bowl with just enough vinaigrette to coat. Divide watercress among 8 chilled plates. Top with orange segments and onion rings. Drizzle vinaigrette around each salad. Garnish with chives. Makes 8 servings.