President's Address. 305 



of the contents of the corpuscle, i.e., the additional matter, 

 such as starch, &,c., present in the corpuscle, the whole 

 being the chlorophyll apparatus. 



As to the nature of the chlorophyll apparatus : — and 

 first the skeleton. Earlier observers held this to be a 

 vesicle. Treviranus first spoke of it as a proteid mass 

 permeated by a green colouring matter, but Von Mohl laid 

 the foundation of our rational knowledge indicating difte- 

 rent characters of corpuscles, and enunciating their solid 

 nature. His views have been accepted generally until 

 Pringsheim's work appeared. 



The chlorophyll itself, in the days of the vesicular 

 theory regarded as a fiuid enclosed in the vesicle, has now 

 generally come to be recognised as a substance permeating 

 the corpuscle. This view Pringsheim modifies. The 

 chlorophyll colouring matter can easily be removed in 

 solvents such as alcohol, and has definite physical charac- 

 ters. Its spectrum is a distinct one, the most prominent 

 absorption bands lying in the more refrangible part of the 

 spectrum, seven bands being recognised. It also, as 

 Brewster first fully demonstrated, possesses the power of 

 fluorescence. Of its constitution we are still much in the 

 dark, notwithstanding many investigations both by chemi- 

 cal and by spectral analysis. In earlier times regarded as 

 a single chemical substance, Fremy first suggested its 

 compound nature, but his investigations, like those of 

 Filhol, Jodiu, and others, are valueless on account of the 

 methods of experimentation followed. N. J. C. Miiller 

 proved the existence of different pigments in chloro- 

 phyll, and in later times Stokes, Kraus, Sorby, Wiesner, 

 and others have attempted to arrange the constituent 

 pigments in groups, and to give them distinct names with 

 an approximate composition. Much controversy has taken 

 place, but the general result has been the recognition of 

 two series of pigments, a yellow (Xanthophyll) and a blue 

 (Cyanophyll), each of which is made up of several minor 

 groups, and these combined form the chlorophyll colouring 

 matter which can be extracted from the corpuscle. In its 

 chemical composition it contains carbon, hydrogen, oxygen, 

 and nitrogen ; Sachsse, from his recent investigations, 

 holding that the cyanophyll series alone contain nitrogen. 



