Only the newly synthesized DNA strands are labelled (with tritium-fluorinedeoxyuridine) since synthesis takes place in the presence of labelled nucleotides. Several replication units can be recognized on the pictures. Pairs of newly synthesized strands hint at the replication of complementary parental strands (explanation). The incubation time was the same for all three samples. The different lengths reflect the different velocity of replication that is specific for each species (a. Vicia faber, b. Vicia hirsuta, c. Vicia sativa). (J.P.GADDAPATI and S.K.SEN, 1978).