A substrate that is suitable for an EUV mask or an EUV mask blank and excellent in flatness, is provided. Formed in an inner peripheral surface of the outer cylindrical body 4 is a recessed portion 42 which becomes concave with clearances C1 and C2 of respective given amounts left between the recessed portion 42 and the projecting portion 52. The invention further relates to methods for producing a lettuce plant containing in its genetic material one or more transgenes and to the transgenic lettuce plants and plant parts produced by those methods. The base recess has a first configuration and the cover layer aperture has a second configuration that is different than the first configuration.