In 1926, after his degree, he worked on hybrid wheat and "Zea mays". In 1931 he was awarded a National Research Council Fellowship at the California Institute of Technology at Pasadena, where he remained from 1931 until 1936. During this period he continued his work on Indian corn and began, in collaboration with Dobzhansky and Sturtevant work on crossing-over in the fruit fly, "Drosophila melanogaster".