Gustav Gassner (born January 17, 1881 in Berlin; died 5 February 5, 1955 in Lüneburg) was a German botanist and plant pathologist whose 1918 paper on vernalization has been called "the first systematic study of temperature as a factor in the developmental physiology of plants."His wide-ranging research interests in phytopathology and plant physiology included work on photosynthesis and plant nutrition as well as practical work on plant diseases such as rust and smut.His classic text from 1931 Mikroskopische Untersuchung pflanzlicher Lebensmittel und Futtermittel ("Microscopic examination of plant foods and beverages") is still in use in German universities and is still referred to by German students as "Gassner."