 Similar work by Lewis Stadler also showed the mutational effect of X-rays on barley in 1928, and ultraviolet (UV) radiation on maize in 1936.The effect of sunlight had previously been noted in the nineteenth century where rural outdoor workers and sailors were found to be more prone to skin cancer.Chemical mutagens were not demonstrated to cause mutation until the 1940s, when Charlotte Auerbach and J. M. Robson found that mustard gas can cause mutations in fruit flies.