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Biol Bull 115: 81-100. (August 1958)
© 1958 Marine Biological Laboratory
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AN EXOGENOUS REFERENCE-CLOCK FOR PERSISTENT, TEMPERATURE-INDEPENDENT, LABILE, BIOLOGICAL RHYTHMS

FRANK A. BROWN JR. 1

1 Department of Biological Sciences, Northwestern University, Evanston, Illinois

1. Oxygen-consumption was monitored almost continuously in potatoes, Solanum tuberosum, in constant conditions, including pressure, for more than two years. A paralleling 8-month study of O2-consumption in carrots, Daucus carota, was also made.

2. The potatoes showed an essentially bimodal mean daily cycle with an average amplitude of the major maximum of 3.7%. The cycles for the two years taken separately were very closely similar.

3. The daily cycle exhibited an annual cycle of form change, with cycles unimodal, inverted, with a 7 PM maximum in February and unimodal with an 11 AM maximum in October. The intervening months yielded bimodal cycles, with graded transitional forms.

4. The daily cycle and its annual fluctuation in the carrot resembled in great detail those obtained concurrently for the potato.

5. An annual cycle in average daily rate of O2-consumption was found in the potato. The cycle was essentially sinusoidal with minimum in October-November and maximum, the rate about doubled, in April-May.

6. Throughout the two years the 5-6-7 AM deviation in O2,-consumption from linear daily trend was always correlated with the 2-6 AM mean rate of barometric pressure change for the same morning. The sign of this correlation exhibited a characteristic change twice each year, once in the spring and again in the fall.

7. For the two-year period of study the amplitude of the daily cycles showed a linear correlation with the concurrent outside air-temperature, with the sign of the correlation reversing about 57.5° F. With temperature expressed as deviation from 57.5° F., the coefficient of correlation was – 0.51 ± 0.049.

8. The data suggest the existence of a rhythmic component of sidereal-day length in the potatoes. Problems in its final resolution are discussed.

9. The evidence points quite conclusively to the possession by the organism, even in so-called "constant conditions," of environmentally imposed oscillations of the natural, daily and annual periods.

10. The fluctuations in the still unidentified, external effective factor appear importantly influenced by, and may possibly even in some measure determine, meteorologic changes of temperature and pressure.

11. The significance of these findings for the problem of the mechanism of the basic daily and annual biological "clock" regulating in "constant conditions" the well-known endogenous organismic rhythms is discussed at some length.




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F. A. Brown Jr.
Living Clocks: The clocks are accounted for as "open systems" depending upon subtle geophysical rhythms
Science, December 4, 1959; 130(3388): 1535 - 1544.
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