Jenny Hempel (19 February 1882 – 13 February 1975)[1] was a Danish plant physiology pioneer. In 1916, she was the first Danish woman to receive a doctoral degree in a botanical discipline – and until 1956, she was the only. She discovered the diurnal fluctuations in cell sap acidity in succulent plants, which are now known to be linked with the CAM photosynthetic pathway.