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We analyzed, under laboratory conditions, the physical effects of smooth and rugose soil crusts on the germination of Mimosa luisana (Legummosae) and Myrtillocactus geometrizans (Cactaceae), two dominant species of plants in the Tehuacan Valley, a semiarid zone in central Mexico. In addition, effects of these crusts on the early seedling growth of M. geometrizans were also analyzed. Our results suggest that biological soil crusts have a positive effect on the seed germination of these plants. However, results about the effects of crusts on seedling growth showed no clear differences between treatments with and without crusts. More studies should be conducted, both in field and laboratory, to completely understand the factors that determine the effects of biological soil crusts on seed germination and seedling establishment of these plants. (c) 2005 Elsevier Ltd. All rights reserved.