1. The two k fragments in a plant of Secale cereale with 16 chromosomes fail to pair in a proportion of pollen mother-cells. Their chiasma frequency and that of their long and skort arms is approximately proportional to their length. 2. Terminalisation is, as expected, more complete in the fragment pair than in the major chromosomes. 3. There is a negative correlation (-0.330) between the chiasma frequency in the major chromosomes and that in the fragment pair of the saure nucleus. 4. The saure plant with otherwise normal pairing had a group of eight cells each showing a ring or chain of four chromosomes. Spontaneous interchange must have taken place in a common ancestral mitotic nucleus. I have to thank Prof. Kihara for the facilities kindly placed at my disposal while carrying out this work in his department. I am also indebted to Prof. Takezaki for advice an statistical treatment.