/4 J. HKHMKKT lAVLoH 



crllular i)i)()l of thyiiiidinc and it.- (lcii\-ati\-('s i> >iiiall in nio.-t cells, (ho 

 rcniDval of the lal)el after one eycle of re))li('ation would allow one to 

 follow the distribution of labeled DNA through several division cycles 

 and tliei"el)y distinguish a >enii-('onsei\'ati\-e replication from the disper- 

 sive one. 



The results for root cells of \'ici(i weic clear (Fig. 2A). After one or 

 a part of a cycle of duplication with thyniidine-H'', the two chromosomes 

 descended from an original unlabeled one were both labeled (Taylor 

 et al., 1957). After one more duplication in the absence of the labeled 



Fiu. 2A. Aulonuliognuu of Vicia cliroino.sunie.s at division after one replication in 

 which thymidine-H' was incorporated into the DNA. Fig. 2B (see facing page). 

 .\utoradiogram of a .<5imilar sroup of chromosomes after one replication with thymi- 

 dine-H^ and one additional iiiiluatioii iii an environment free of labeled precursors 

 of DNA (X 3200). 



