Abstract
1. Detailed cytological analysis at diakinesis and metaphase I in Zebrina pendula Schnizl., (n=12) showed that about 47.65% of the cells examined contain higher associations of rings and chains of 6 and 4 and chains of 3 chromosomes. More than two such higher associations per cell or more than 6 chromosomes per association were not observed. The rest of the chromosomes formed into bivalents and univalents.2. The differences in the sizes of the chromosomes in the higher associations, pachytene configurations with cross-shaped figures and formation of associations of 6's in a plant showing only a tetraploid chromosome number confirm that these higher associations are formed as a result of reciprocal translocations between nonhomologous bivalents.3. Univalents formed as a result of failure of chiasma formation or nondisjunction of higher associations at anaphase I either divided or undivided reach the poles or lag behind and organize into micronuclei which were usually met with from dyad stage to pollen grains.4. Bridges with or without fragments were found in a low percentage of cells at anaphase I and II and telophase I and II. Pollen sterility is very high.5. The divergent cytological behaviour of Z. pendula investigated by various workers is believed to be due to geographical variations under the influence of which the plants of this species are undergoing chromosome evolution with differential rapidity by spontaneous structural rearrangements in the somatic chromosomes.6. Colchicine induced tetraploid Z. pendula (n=24) formed mostly bivalents and this prevalent bivalent pairing was explained in terms of preferential pairing between the exactly identical partners of chromosomes furnished by the duplicate genome. This suggests that all the chromosomes in the diploid are structurally dissimilar to some extent or other and in the absence of completely homologous partners the unlike chromosomes resort to pairing in the diploid.
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