Diurnal course of the temperature in a Lithops sp. (Mesembryanthemaceae Fenzl) and its surrounding soil

. The embedding of Lithops plants into the soil could be an adaptation to protect the plants from critical low or high temperatures. Thermoelectric measurements on Lithops lesliei N.E. Br and L. turbiniformis (Haw.) N.E. Br. were made to determine whether the temperatures of the plant tissues at various depths differ from those in the soil close to the plant. The environmental conditions of their habitat were simulated in a growth chamber equipped with a cold sky to simulate the net radiation loss during a cool and clear night. The effects of microclimatic conditions resulting in dew or hoar‐frost formation on the plant were investigated, as well as the temperature range where freezing occurs. The results provide no evidence that the embedding of a Lithops plant into the soil yields advantages to the plants in respect of critical low or high temperatures. Plant temperatures are always very close to the soil temperatures at the same depth, but heat fluxes from the bottom or the plant and its surrounding soil to the top of the plant can occur if the plant freezes. No positive effect on the temperature relations could be detected when dew or hoar‐frost is formed on the top of the plant. Lithops is frost hard to at least –3°C.