Schimper pioneered research in the field of plant morphology, particularly phyllotaxis. The flowers of Berberidopsis have a spiral phyllotaxis. Bravais also studied magnetism, the northern lights, meteorology, geobotany, phyllotaxis, astronomy, statistics and hydrography. The phyllotaxis or leaf arrangement can be spiral or subopposite and nearly decussate. Examples of trees with whorled phyllotaxis are "Brabejum stellatifolium" and the related genus "Macadamia". The phyllotaxis or leaf arrangement is spiral and may be subopposite on some shoots. Crassulaceae Decussate phyllotaxis also occurs in the Aizoaceae. The phyllotaxis or leaf arrangement is usually spiral but may be opposite on young plants. A. H. Church studied the patterns of phyllotaxis in his 1904 book. These models are called "up-the-gradient" models and explain for instance phyllotaxis. Physical models of phyllotaxis date back to Airy's experiment of packing hard spheres. Phyllotaxis has been used as an inspiration for a number of sculptures and architectural designs.