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To the Editor:—
Biological timing does not begin and end with a phrase, nor is it a simple mechanism. In algae a synthetic photoperiodism can be established by exposing them to regular periods of light and darkness, which will continue for weeks even in enucleate fragments. This is a phenomenon of intracellular metabolism in Acetabularia, as Brachet reports in detail, where DNA is involved in the biological clock (Endeavour24:155, 1965). His experiments show that the nucleus of the cell supplies something essential, and that there is a delicate interaction between the messenger RNA formed in the nucleus and the chloroplasts. The normal rhythm of multiplication of the chloroplasts is slowed after removal of the nucleus. "Circadian" if you like, but let's start the rhythms off correctly, within the cell. Biological clocks in hamsters have been found geared to something close to lunar time periods, and influences of light
Liddle GG. Circadian Rhythms. JAMA. 1966;196(1):108. doi:10.1001/jama.1966.03100140162060