Taylor et al. (1957) conducted experiment on Vicia faba (broad bean) to prove semi-conservative replication of DNA. He fed dividing cells of root tips of Vicia faba with radioactive ³H containing thymine instead of normal thymine and found that all the chromosomes became radioactive. Labelled thymine was then replaced with normal one. Next generation came to have radioactivity in one of the two chromatids of each chromosome while in subsequent generation radioactivity was present in 50% of the chromosomes. This is possible only if out of the two strands of a chromosome, one is formed afresh while the other is conserved at each replication.