We examined the solid-state structures of two cylinder-forming semicrystalline diblock copolymers, where polyethylene forms the continuous matrix in both, using simultaneous small- and wide-angle X-ray scattering combined with transmission electron microscopy. The mesophase structure formed in the melt is largely retained upon cooling, whether the cylinders are glassy or rubbery during crystallization. Specimens in which the cylinders had been macroscopically oriented by flow revealed that the hexagonal packing of cylinders induces an unusual two-dimensional preferred orientation of the polyethylene crystals within the matrix. Specifically, the crystals tend to grow with their b axes parallel to the cylinder axes, while in the plane of the cylinder radii, the crystals tend to align their c axes parallel to the (10), (01), and (11) planes of the hexagonal macrolattice. By calculating various dimensions within the macrolattice, we conclude that the observed orientation allows the E crystals to best adopt their preferred thickness and spacing.