1. Further studies on chromosome knobs of South American varieties have shown that the majority of varieties from Peru, Bolivia, and Ecuador have knobless chromosomes. This supports our previous suggestion that the Andean region, which we regard as the primary center of domestication of maize, is the only region where pure maize has not been largely replaced by Tripsacum-infected varieties. If this is true most of the stocks of North American maize with which the majority of genetic and cytological studies are conducted are probably polyploid for certain regions of the chromatin. This may account for the fact that some very minute deficiencies are quite deleterious while other larger deficiencies have no appreciable effect.