The study was carried out to unravel the in vitro cytological behaviour of leaf callus cultures of Orthosiphon ariststus (Blume) Miq. The cultures were raised using leaf explants on Murashige and Skoog (MS) medium supplemented with different growth regulators like auxins (2,4-D, IAA, NAA) and cytokinin (BAP) alone and in different concentrations and combinations. Best callusing from the leaf explants was achieved in 2,4-D supplemented MS medium at 5 mg/l concentration. Cytogenetic analysis of

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... e chromosomal variations was carried out for primary cultures as well as 3-month-old callus cultures. The chromosome number did not show variations and the cells studied were observed to be diploid (2n= 28) in nature. Among the numerical observations induced, polyploid cells were the most frequent. The frequency of bridges was observed among the other structural changes. The composition and concentration of the growth regulators was found to affect Dorothy et al.; BBJ, 13(4): 1-6, 2016; Article no.BBJ.25638 2 chromosomal instability with multinucleate, multinucleolate and embryogenic masses. These observations indicate that genetic variations may arise during cell cultures. Original Research Article