Abstract: It was suspected that differences in style length and other reproductive structures of tetraploid and diploid cottons may contribute towards failure of crossing between two ploidies. Style length, stigma depth and pollen grain size of tetraploid were 20.5, 60.0 and 10.0 mm against 8.5, 2.0 and 7.0 mm of G. harknessii and 9.0, 2.5 and 7.0 mm of G. arboreum respectively. In vitro germinated pollen tubes of both the ploidy levels also varied significantly where tetraploid produced pollen tubes upto 20.5 mm long against 8 to 9.0 mm pollen tubes of both diploid species. It was therefore confirmed that style length is highly correlated with pollen tube length. Thus, shorter pollen tubes of diploid species are not expected to grow long enough in the longer styles of tetraploids and reach the ovary to fertilize it. Since, pollen grain size and stigma depth are also considered as food reserves for pollen tubes to grow into the styles and the differences in these structures can also be accountable to the failure of fertilization between the ploidy levels. Based on these results, it can be predicted that differential reproductive structure could at least be partially responsible for crossing failure and reciprocal crosses may be tried for successful fertilization.