Measurements of CO2 compensation were made over long periods of time for Coffea arabica and Bryophyllum daigremontianum. For each species there was a marked rhythm in the level of CO2 compensation, even though all major factors of the environment were held as constant as possible. The rhythm in Coffea was susceptible to phase-shift and had a period slightly greater than 24 h. The rhythm in Bryophyllum had a period of c. 23 h. These observations show that the rhythm is probably endogenous in nature.
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Jones et al. (1970) studied this question.