Heterosis in Inbred Source Crosses of Maize (Zea mays L.)1

This study was designed to determine the variability within maize (Zea mays L.) lines maintained at different stations in the northern maize‐growing areas of the U. S., with particular attention to heterotic expression in withinline crosses. There was significant variation in the various characteristics studied in most of the lines, although certain characteristics such as kernel row number and ear diameter showed considerable stability. The information should be of particular interest to seed producers and certification agencies where variation within lines could have serious consequences or could be used to an advantage in production of related‐line single crosses.