Carbon dioxide uptake by succulents

Carbon dioxide absorption by a selection of succulent plants, was followed by a modification of Tregunna's method, in which the plant sample on absorbing the carbon dioxide from an enclosed volume of air in contact with weak bicarbonate, causes the solution's pH to change. Of the 21 species tested, 11 took up carbon dioxide in the dark: Lithops turbiniformis, Zygocactus truncatus, Bryophyllum daigremontianum, Crassula multicava, Echeveria gibbiflora, Kalanchoe blossfeldiana, Sedum confusum, S. pachyphyllum, S. rubrotinctum, S. spectabile, Aloe globuligemma. The duration of uptake varied from a few hours to the whole night (and longer). Even in those other species where uptake occurred in the daytime it started and stopped at times not immediately related to the onset of light or darkness.