RESPONSE OF A LIVING ORGANISM, UNDER "CONSTANT CONDITIONS" INCLUDING PRESSURE, TO A BAROMETRIC-PRESSURE-CORRELATED, CYCLIC, EXTERNAL VARIABLE

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

1. Fluctuations in O₂-consumption in the potato under constant conditions, including pressure, were observed. The average solar-day cycle was determined and this was found to have in large measure a form which was the mirror image of that obtained during the same months of the preceding year.

2. The average lunar-day cycle was also determined and this, too, was in its principal features an inversion of that found for the same period of the preceding year.

3. A study of the patterns of daily variation for the 154 complete days of data revealed that all the patterns of fluctuation on any given day tended to exhibit a generic similarity to one another, tending to exhibit either parallel, or mirror image fluctuations, and of the same general amplitude.

4. All the daily patterns could be divided in two groups. One group (99 days) called the positive one (since its later discovered correlation with barometric pressure change was positive) possessed a maximum about 6 A.M. and a minimum about 9 A.M.; the negative group (55 days) tended to show the mirror image of this form in the daily period 4 to 11 A.M.

5. The deviation in rate of O₂-consumption from the daily mean for the positive group for the 4-7 A.M. period was found to show a positive correlation with the algebraic sum of the rates of change in barometric pressure during the three preceding 2-4 A.M. periods; the negative group, on the other hand, showed a negative correlation for the comparable relationship.

6. A correlation between the deviation from the daily mean of O₂-consumption at the 4-7 A.M. period and the algebraic sum of the pressure changes for the three preceding 2-4 A.M. periods was found for all 154 barostat-days if one ignored the sign of the deviation in rate of O₂-consumption, proving true an earlier hypothesis that the sign of the response of the organism to an external pressure-correlated factor changed from time to time.

7. The deviation from the daily mean of O₂-consumption for the 4-7 P.M. period showed a negative correlation with the algebraic sum of the rates of barometric pressure change for the preceding three 2-4 P.M. periods, and the 10-1, midnight deviation, was correlated with the three-day pressure-change from 8-12 P.M.

8. Since it was demonstrated that the correlations were not with single days of an external factor, nor with any averaged three-day periods other than the three immediately preceding daily periods, it was evident that the potatoes were deriving an essential element of the form of their daily fluctuation from a response to an external factor which, since pressure-correlated, clearly possessed average solar-day cycles.

9. The external factor appears to determine in the daily fluctuation of O₂- consumption the amplitude of a morning oscillation (or its mirror image) with about a six-hour period, the height of the late-afternoon maximum, and probably also the extent of the midnight reduction in rate.

10. Possible relationships of the exogenous to endogenous cycles are discussed briefly with reference to the problem of biological clocks.