A variety of plant species and cultivars were stained for chromocenters using the barium hydroxide, sodium saline citrate (SSC), Giemsa procedure (DNA denaturation, incubation-renaturation, staining), in order to test the hypothesis that larger (biomass) species have larger, more numerous, and more intensely-staining chromocenters. In all species and cultivars examined, results confirmed the hypothesis. Since chromocenters are believed to be composed primarily of heterochromatin/repetitive DNA (which has been postulated to shorten the cell cycle), it is likely that chromocenters modulate species size/biomass. Among closely related species, larger/more biomassive cultivars contained larger, more numerous, and more intensely-staining chromocenters than smaller/less biomassive cultivars.