Cytological Studies inBegonia— II

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Abstract
The present paper deals with the cytology including karyotype analysis of eight species and varieties of Begonia, viz. B. paupercula King, (2 n = 22); B. rex Putz., (var. I), (2 n = 22); B. rex Putz. (var. II), (2 n = 32); B. rex Putz. (var. III), (2 n = 34); B. malabarica Lam., 2 n = 28); B. laciniata Roxb. (var. I), (2 n = 20); B. laciniata Roxb. (var. II), (2 n = 22); B. sp. (unidentified), (2 n = 28). In addition to these two varieties B. gigantea Wall., and two varieties of B. semperflorens, were observed. One of the former two varieties showed 2 n = 28, 32 and 34 chromosomes and in another 2 n = 40 and 42 chromosomes were counted in the somatic tissue and the latter in meiosis showed 40 to 46 chromosomes. The implications of such aneuploid numbers have been pointed out. The chromosomes are graded and in all the different species and varieties taken together with their general morphological features can be divided into eleven distinct types. Variation in addition to normal chromosome number has been observed in large number of dividing cells. These are either lower or higher than the normal number. In case of B. B. laciniata, variation complement of one variety has been found to be the normal number for another variety of the same species. Meiotic studies on five species show high frequency of meiotic abnormalities. However, a variety of B. rex and B. paupercula showed comparatively low irregularities. Variations in meiosis have also been met with, which directly correspond to somatic variations. As a result of aberrant divisions, pollen sterility has been recorded to be very high (60%–70%). Importance of somatic variations in the evolution of different species as discussed in a previous communiqué, has further been emphasized specially with reference to direct evidences obtained in B. laciniata. The cause of successful retention of the variation numbers within the somatic tissue has been discussed and the possibilities of their ‘accessory’ nature along with evidences for the same has been pointed out. The phenotypic differences within the cytotypes have been suggested to be due to the fact that alterations in such cases may involve one or two chromosomes in addition to some accessory ones. The significance of continued vegetative propagation and migration of altered nuclei in the development of a new individual in speciation has been discussed.