To gain a better understanding of seasonal photosynthetic patterns, main stem cotton leaves were monitored for photosynthesis (AP), soluble protein, ribulose bisphosphate carboxylase (RuBisCo) and chlorophyll (CHL). The recently emerging leaves were tagged at two week intervals starting at 48 days after planting (DAP) and ending at 89 DAP. The tagged leaves were randomly measured at weekly intervals until no leaves of a particular age could be found.