Abstract
1. Mature hybrids were raised from P. mungo _??_ × P. calcaratus _??_ cross by culturing the embryonic axes of the hybrid seeds in nutrient solution with 4 per cent sucrose.
2. The F1 plants resembled one or the other parent in some characters and were intermediate between them in others. These plants had an average pollen fertility of 0.7 per cent and did not set pod.
3. In F1, the average chromosome configuration per cell at MI was 0.05IV+4.24II+13.32I. One quadrivalent was noted in 5.1 per cent of cells. Dicentric bridges with acentric fragments were noted in 3.3 per cents of cells at AI. Dicentric bridges were observed in 4.7 per cent of cells at AII. At pachytene, some loosely paired bivalents with terminal and interstitial differential segments were noticed.
4. Colchicine induced amphidiploid (AI generation) plants had an average of 81.0 per cent fertile pollen and they produced few pods with viable seeds.
5. The role of hybrid inviability, weakness and sterility as isolating barriers has been discussed. The hybrid sterility is segregational in nature. The significance of structural alterations in speciation has been discussed.
