Metabolic Aspects of Thermogenesis in Male Cones of Five Cycad Species

High starch concentrations in the sporophylls of male cones of five species of cycad and their depletion during their heat‐producing phase of development suggest that starch is a major fuel source for thermogenesis in these plants. Carbon‐13/carbon‐12 ratio analyses of respired CO 2 , starch, and lipids in a male cone of one of these species, Macrozamia moorei F. Muell., indicate that although starch is a major contributor to respiration, lipids are also an important respiratory substrate.