1. V3 is located on the longer arm of chromosome 5, not far from the insertion region. This is the cytological position of Df 51, which includes V3. Linkage data indicate the Df is between Bm1 and Bv, very close to Bv. The Df does not include Bm1, Bt, or Bv. This internal deficiency markedly reduces crossing over, both in the Bm-Bv region and in the Bv-Pr region. This shows that in maize crossing over may be inhibited by deficiency outside the region homologous to the Df, which appears not to be the case in Drosophila.