The chromocentres in nuclei of germinating radicles ofBryonia dioicanormally disperse before the onset of DNA synthesis. Inhibitors of DNA synthesis enhance the frequency of such disperse nuclei. Later, when the meristem of the rootlets is established, there is a good correspondence between the disperse Z phase morphology and DNA synthetic activity in such nuclei. When roots are exposed to inhibitors of DNA synthesis Z phase persists but the correspondence with DNA synthesis is broken. It is proposed that chromatin dispersion is not dependent upon DNA synthesis, and that chromatin condensation/decondensation and DNA synthesis are markers of two separate cyclical processes that occur in proliferating cells.