Once the Fibrograph method to determine maturity in cotton fiber was adopted at the Instituto Agronômico (Campinas, State of São Paulo, Brazil), the need of specifïc standard limits for the several classes of maturity, based on this process, was recognized. In effect, despite of the observed correlation between the results obtained by this method and those revealed by the NaOH process, which enables one to express the Fibrograph indices in terms of percentages of mature fibers, the inadequacy of assessing the results, based on the standard USDA scale for the caustic soda method was soou verified. Actually, if this scale was considered, the great majority of fibers submitted to analysis should be classified as immature. Thus, a study was carried out in order to define a more suitable scale, based on the data originally used to establish the Fibrograph Method. A normal curve (x = 12.57; s = 1.46) was fitted to 59 data of fiber maturity, which includes different genetic materiais as well as diverse environmental conditions, comprising, therefore, a broad range of maturity. Due to the goodness of fit (X2 = 4.57; 5% = 11.07), the percentiles 10, 30, 70 and 90 in the normal curve were chosen and defined as the standard limits, respectively, for the classes "very low", "low", "medium", "high" and "very high" maturity. If Fibrograph indices are to be used to express the results, the limits of such classes were found to be 14.57, 13.40, 11.79 and 10.67, respectively. The correspondent values, if percentages of mature fibers are considered, are, aproximately, 45, 52, 63 and 72%.
cotton; fiber; maturity; Fibrograph; classification