Muro-Pérez G., Jurado E., Flores J., Sánchez-Salas J., Effect of seed burial in different soils on the germination of three specially protected cactus species, The Southwestern Naturalist, 2014, 59(3):344-348, doi: 10.1894/MLA-06.1
A germination experiment on Coryphantha durangensis, Peniocereus greggii and Echinocereus longisetus. It compares seeds on the surface and beneath a soil layer, in substrate from beneath mesquite and from open spaces. It shows how germination depends on seed position and soil origin, with different species responses.