Morphology and pairing behaviour of the pachytene chromosomes in a tetraploid race ofS. arundinaceumwas studied on a quantitative basis. The study showed the chromosomes to be differentiated and that the 10 basic types characteristic of the diploid grainSorghumscan be recognised in the tetraploid. In a total of 131 pachytene associations studied the frequency of exchanges vary from none to two in a given set of four pairing chromosomes. Further the exchanges appear to have been spread out all along the length of chromosomes. From the evidence obtained and the regular meiosis observed in the polyhaploid derivative of this plant it was suggested that the tetraploid understudy had an autoploid origin.