THE green colouring matter of plants is a wax-like material of complex chemical structure to which the name chlorophyll was given by Pelletier and Caventou in 1817. It is insoluble in water but soluble in alcohol, ether and other organic solvents. Early investigations of chlorophyll which are important are those of Brewster and Stokes, on the absorption spectrum and fluorescence, and of Edward Schunck on the chemical side. Schunck studied particularly the action of acids on chlorophyll and found that important changes in its physical and chemical properties resulted. The first really fundamental investigations on the chemical structure of chlorophyll were those of Willstatter and his collaborators1 which showed that there are two green pigments present in leaf-green, namely, chlorophyll-a, with the formula Cg2H2Og2Mg, a bluish-black solid giving greenish-blue solutions; and chlorophyll-6, a greenish-black solid giving pure green solutions.