In this paper, the literature on, the origin and growth of reversal extinction bands in cotton fibres, as observed along their lengths in crossed polarized light in a polarizing light microscope, has been briefly reviewed and extensive data on the frequency of reversal/extinction bands in field matured fibres of a large number of the same cotton varieties, grown at four different locations of growth in India, are presented and discussed. It is observed that the frequency of reversal/extinction bands per centimeter length of cotton fibres for the same varieties grown at different locations remain practically invariant, although their value varies between individual varieties. Apparently, reversals/extinction bands observed along the length of cotton fibres,appear to be genetically determined.