<image> (2008 Tianjin Nankai District Quality Inspection 1) As shown in the figure, ornamental plants are planted in areas A, B, C, and D of a tic-tac-toe shaped region. The same type of plant should be planted in the same region, and different plants should be planted in adjacent regions (A and D, B and C are not adjacent). If there are 4 different types of plants to choose from, how many different planting schemes are there? (Answer with a number)