Actively growing young rhizomes of various Alstroemeria cultivars, most sterile hybrids, were treated with X-rays. The optimum dose was about 400 rad for diploid cultivars and 500–600 rad for triploid ones. Although the buds on the rhizomes most certainly have multicellular apices, no X-ray mutant showed any sign of chimerism. Hence only solid(-looking) mutants were obtained. This phenomenon, an unforeseen but advantageous circumstance, could not be explained. Among the rather large number of mutants, several proved to be improvements and have been released to the trade such as cvs. Canaria Stagula, Yellow Tiger Stavero, White Wings Staretto, Harmony Stabroza and Rosita Stareza.