Hans Molisch

Hans Molisch was born on 6 December 1856 in Brünn (now Brno, Czech Republic), then part of the Austro-Hungarian Empire. He studied at the University of Vienna, where he earned his doctorate in 1879 under the botanist Anton Kerner von Marilaun. After a period as a high-school teacher, he became a professor at the German University of Prague in 1894, and later moved to the University of Vienna in 1909, where he served as director of the plant physiology institute until his retirement in 1928.¹

Molisch's most enduring contribution is the Molisch reaction (also called the α-naphthol test), a simple colorimetric test for carbohydrates. He discovered that when a sugar solution is treated with α-naphthol and concentrated sulfuric acid, a violet ring forms at the interface. This test, still used in biochemistry and clinical diagnostics, detects sugars, glycosides, and other carbohydrates.²

He also investigated the phenomenon of phototropism and the effects of colored light on plant growth, showing that blue light is most effective in inducing phototropic curvature. His work on the iron bacterium Leptothrix ochracea clarified its role in the oxidation of ferrous iron and the formation of iron deposits in aquatic environments.³

Beyond his famous test, Molisch made several overlooked contributions. He was among the first to describe the phenomenon of fluorescence in plant tissues, observing that chlorophyll emits red fluorescence when illuminated. He also studied the effect of mechanical stimulation on plant growth, a field later developed by others. In 1913, he published a monograph on the anatomy and physiology of the plant cell, which was widely used as a textbook. He also coined the term "photodinesis" to describe light-induced cytoplasmic streaming.⁴

Molisch was elected a member of the Austrian Academy of Sciences and received honorary doctorates from several universities. His textbook Pflanzenphysiologie als Theorie der Gärtnerei (Plant Physiology as a Theory of Horticulture) influenced practical horticulture. The Molisch test remains a standard procedure in sugar analysis, and his name is commemorated in the genus Molischia (a group of green algae).⁵

Molisch reaction

A colorimetric test for carbohydrates using α-naphthol and sulfuric acid, producing a violet ring.

Phototropism

The growth of a plant organ in response to light direction.

Iron bacterium

A microorganism that oxidizes ferrous iron to ferric iron, often forming ochreous deposits.