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Cell and nuclear volumes were determined for 17 species and plant types in the genus Gossypium. All species and types, except one, showed a significant positive association between nuclear and cell volume. The overall species r-value (0.694) for cell and nuclear volume is highly significant and positive. For the 17 plant forms, the r-values for association of DNA content and nuclear volume and for association of DNA content and cell volume are 0.625 and 0.655, respectively, and both are highly significant.

The DNAs of two diploid species of Gossypium, G. herbaceum var. africanum (A1 genome) and G. raimondii (D5 genome), and the allotetraploid species, G. hirsutum (Ah and Dh genomes), were characterized by kinetic analyses of single copy and repetitive sequences. Estimated haploid genome sizes of A1 and D5 were 1.04 pg and 0.68 pg, respectively, in approximate agreement with cytological observations that A genome chromosomes are about twice the size of D genome chromosomes. This differences in genome size was accounted for entirely by differences in the major repetitive fraction (0.56 pg versus 0.20 pg), as single copy fractions of the two genomes were essentially identical (0.41 pg for A1 and 0.43 pg for D5). Kinetic analyses and thermal denaturation measurements of single copy duplexes from reciprocal intergenomic hybridizations showed considerable sequence similarity between A1 and D5 genomes (77% duplex formation with an average thermal depression of 6 °C). Moreover, little sequence divergence was detectable between diploid single copy sequences and their corresponding genomes in the allotetraploid, consistent with previous chromosome pairing observations in interspecific F1 hybrids.