Discussions Secondary AssociationThe association of bivalents at meiosis was first observed by Kuwada (1910) in Oryza sativa only in second metaphase. Ishikawa (1911) found secondary pairing also at first metaphase of Dahlia variabilis . Since then various authors have found this phenomenon in different genera. Darlington (1928) originally advocated the theory of secondary pairing in his studies on Prunus. It was put on a systematic basis by Lawrence (1931) who has discussed all the known cases of secondary pairing. Secondary associa tion can be used as a measure of distant relationship between the chromo somes present in a polyploid, and it will be so used in determining the basic composition of the chromosomes in genera Eleusine, Dactylocteniuin, and Setaria. Heilborne (1937) discussed his impressions on secondary association and considered that such associations have purely mechanical origin. Ac cordingly chromosomes of equal size are associated irrespective of homology. In genera Eleusine, Setaria and Dactyloctinium, however, it was noticed that the secondarily associated chromosomes were not identical in size in all cases. Alam (1936) in Brassica compestris, Riccharia (1937) in Brassica and Iyenger (1939) in Cicer also have recorded secondary associations between short and long bivalents. Thomas and Revell (1946) by their study on secondary association of heterochromatic attraction on Cicer arietinum have come to the conclusion that the fusion between the highly charged heterochromatic regions of dif ferent bivalents at pachytene is responsible for the characteristic inter-bivalent secondary association at metaphase. They however, find inter-bivalent con nections only in nuclei which were less diffused than usual. No such con nections were found by them between the affected bivalents throughout the meiosis. They further maintain that entirely satisfactory evidence of the persistence of the connections could not be obtained in C. arietinum but make assertion that confirmatory evidence of real connection from their work on turnip. This work has not been published yet since then and thus can not warrant any certainity of opinion. Nothing like any such physical con nections is noticed in the grass materials (microphotographs).Thus by studying the secondary association at metaphase I and II in genera Eleusine, Dactyloctinium and Setaria, assuming that structural changes Cytologia 24, 1959 11 150 R. P. Chandola Cytologia 24have taken place the haploid genoms can be represented as follows:-E. indica, E. verticillata and S. italica are usually regarded as diploids but the cytological data support the view that these are secondarily balanced species in nature.According to the opinion of the author the immediate wild progenitors of these are unknown and perhaps exist no more. E. coracana, D. aegepticum, S. glauca and S. verticillata are thus secondarily balanced polyploid species.
Species differentiation in Chlorideae and PaniceaeAs regards the factors involved in the differentiation of species in the tribes Chlo...
