Measurments of total nucleic acid content of the embryonic axis indicated that massive net synthesis of both DNA and RNA was initiated at approximately 30 h after the onset of germination. The onset of net nucleic acid synthesis was marked by an increase in the rate of incorporation of [(3)H]thymidine into DNA, and of [(3)H]orotic acid and [(3)H]uridine into both DNA and RNA. rRNA was usually more heavily labelled than tRNA, but was not preferentially accumulated, suggesting a grater rate of turnover of rRNA than tRNA. Some incorporation of precursors occurred prior to the onset of net nucleic acid synthesis, particularly into RNA. This was taken to represent nucleic acid turnover. There was no evidence that the "scavenging" pathways for nucleotide biosynthesis were more important than the "normal" pathways in contributing precursors for net nucleic acid synthesis.