In the progeny of crosses between plants with the chromosome number 2n=13+2 telocentrics as the male parents and the normal diploids of Pennisetum typhoides S. & H., two plants with 2n=13+1 telocentric chromosome were located. These two plants were heterozygous for an interchange, since at diakinesis and metaphase I associations of four chromosomes were observed. These plants had a chromosome constitution of 2n=13+t (or 6″+tI″); one chromosome of a homologous pair was represented by a telocentric chromosome so was monosomic for one arm, that is, these plants were "monotelodisomics" (Kimber and Sears, 1968).