Correspondence of banding patterns to 3h-thymidine labeling patterns in polytene chromosomes

3H-thymidine labeling frequencies over X chromosomal region 1A-4E of Drosophila melanogaster, were analysed with reference to chromosome sections with and without prominent bands. A correspondence was found between band sections and late start of silver grain labeling at the initial stage in combination with late labeling at the end stage of replication. A complementary situation is always to be found over puff/interband sections, where an early start of labeling at the initial stage is generally combined with early labeling completion at the end stage of replication.