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Growth kinetics and levels of auxin substances were studied in three cotton cultivars, designated as long, medium and short staple cultivars. Fibre length and dry weight plotted against boll age showed sigmoidal patterns and were fitted to a logistic curve by computer curvilinear regression analysis. The final length of the fibre in different cultivars was the product of the rate of elongation per day and the total period of elongation. Further, considerable overlap between the elongation and the secondary thickening phases was recorded. No relationship between auxin substances and rate of fibre elongation was discernible. The peak levels of auxin substances in all the cultivars were recorded before or about the time when elongation had just started, and it is concluded that the auxin synthesized during the elongation phase is consumed in elongation growth. Thus there is necessarily no relationship between remaining auxin and growth.

Three cotton genotypes "varying in their _nal seed size#\ viz[ H!5 and H!3 "Gossypium hirsutum L[# and V!686 "Gossypium herbaceum L[# were studied for their growth kinetics of seed and _bre[ Both biphasic linear and poly! nomial models were used to demark di}erent phases of cotton seed growth[ The polynomial model appeared to be appropriate to de_ne the growth phases of cotton seed as compared to the linear model[ The rate and the duration of dry matter accumulation were obtained by di}erentiating the best!_t polynomial equations[ Based on the data of dry weight and water content\ cotton seed development is divided into four di}erent phases\ viz[ "a# cell division\ "b# cell elongation\ "c# dry matter accumu! lation and "d# maturation[ The rate of dry matter accumu! lation showed a close correlation with water content of seed as well as of the _bre\ in all three genotypes studied[ It is proposed that water content of seed or _bre plays an important role in determining dry weight of three genotypes[

The relationship between growth and some enzymes of carbohydrate metabolism in developing cotton fibre were studied. Two respiratory pathways of glucose oxidation i.e. oxidative pentose phosphate pathway (OPPP) and glycolysis operates in the elongating cotton fibres and the extent of their operation varies with the demand for respiratory products. In this respect, hexokinase, G-6-PDH, 6PGDH, and MDH show increased activities during the period of rapid cell elongation and decreased activities when rate slows down. The conversion of PEP to malate and/or via a transhydrogenase system consisting of enzymes PEPC, MDH and NADP-MDH(d) may play a significant role in carbohydrate compartmentation of developing cotton fibre. As the rate of fibre growth slows down, a decline in enzyme activities, points to a shift in metabolic priorities. List of abbreviations: DPA = Days post anthesis; d = Day; G 6 P D H = Glucose-6phosphate dehydrogenase; M D H = Malate dehydrogenase; NADP-MDH(d) = NADP-MDH(decarboxylase); OAA = Oaxlo acetic acid; PEP = Phosphoenolpyruvate; P E P C = P h o s p h o e n o l p y r u v a t e c a r b o x y l a s e ; 61PGDH = 6-Phosphogiuconate dehydrogenase; PK = ~),'~_~vate kinase

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