The genus Gossypium has approximately 40 species comprised of 7 diploid genomes and 4 to 5 allotetraploid genomes. The 2 diploid genomes (A and D) are considered to be the putative parents of the allotetraplopids G. hirsutum L. (AD)(1) and G. barbadense L. (AD)(2). The CER values of G. klotzchianum (D3k), G. raimondii (D(5)), G. herbaceum (A(1)) and G. hirsutum (AD)(1) were 31.6, 39.0±3, 38.0±5 and 45.0±6 mg CO₂ dm^-2h^-1 and these are consistent with the CER value determinations of several species of Gossypium by El Sharkawy et al(1965). The level of rubisco activity was 29.1, 29.8, 39.1 and 41.7 mg CO₂ dm^-2 h^-1 for D(3)k, D(5), A(1) and AD(1). Leaf area (cm²) and cell volume (cm³10^-10) were 157.7, 267.3, 33.8, and 100.4 and 17.32, 10.32, 100.5 and 225.5 for D(3)k, D(5), A(1) and (AD)(1). The variation in the level of Rubisco activity per mesophyll cell showed a positive correlation to the amount of enzyme present in the cell when the enzyme was localized in situ by an indirect immunofluoerscence assay.