Hybridised regions between labelled A. tumefaciens Ti-plasmid DNA and Feulgen-positive regions of squashed infected tissues were found by in situ hybridisation studies. Ti-plasmid sequences could only be detected in infected tissues of one, two and, at much lesser extent, 9 days after tumour induction; hybridisation could not be detected in 24-day-old infected tissue with the experimental procedure described. The data obtained suggest that Feulgen-positive nuclear DNA of tumour-cells could be one of the integration sites of Ti-plasmid sequences.
