The meiotic behaviour of chromosomes was studied in four inbred lines and their F 1 hybrids of P. typhoides. The inbred lines showed a decrease in mean chiasma frequency when compared with the population plants, but differed from one another in their mean chiasma frequencies. Together with the decrease in mean chiasma frequency the inbreds showed variation in mean chiasma frequencies. The inbred lines showed a number of meiotic abnormalities such as extra chromosomes, extra fragments, desynapsis, persistent nucleoli and differential condensation of chromosomes. The F 1 hybrids of these inbreds exhibited heterosis for chiasma frequency. All the F 1's had mean chiasma frequencies higher than the means of the respective participating parents. The F 1's, however, differed in the degree of heterosis exhibited. In the F 1 hybrids, the variation in mean chiasma frequency, both between plants and between PMC's within plants, was significantly lower than that of the inbred lines. The effect of environment was studied in the inbred lines and their F 1 hybrids. The mean chiasma frequencies of the inbred lines were significantly lower, and the variation in mean chiasma frequencies was greater, in the stress season. The mean chiasma frequencies of F 1's did not show any significant differences between the two seasons. The F 1's exhibited less variation in mean chiasma frequency than the inbred lines, showing that F 1's were developmentally more stable. The F 1's did not show any meiotic abnormalities in either season.