306 President's Address. 



the xantliopliyll having none. Iron is present in the 

 chlorophyll, and various observers have found organic sub- 

 stances of a fatty and starchy nature in it. 



Of the contents some are visible in the corpuscle, others 

 only after reagents have been applied. Starcli is almost 

 universal ; Pringsheim first, and after him Nageli, proved 

 oil globules to occur ; sugar has been supposed to exist, 

 though never actually proved; and Pringsheim has claimed 

 to have found organic acids. In his new work Pringsheim 

 adds some other substance — " hypochlorin " and " tannin 

 vesicles." 



As to the formation of the chlorophyll apparatus. 

 Firstly, of the corpuscular skeleton. Sachs first distinctly 

 described it as an aggregation of molecules round specific 

 centres (under conditions requisite for growth), which subse- 

 quently become coloured. At a very early period it was 

 urged by Mohl that in some cases the starch particles were 

 the primary factors round which the corpuscle became 

 aggregated, and this view apparently has some warranty 

 from recent investigations by Haberlandt, Mikosch, Stohr, 

 and others into the history of false corpuscles. 



For the development of the colouring matter two external 

 conditions are necessary — (a) Light of not too high or too 

 low intensity. Seedlings of some plants develop chloro- 

 phyll in darkness, this being a primary condition only. If 

 light insuQicient, a blanching is seen,Etiolin being formed, 

 a substance which has given rise to controversy ; Kraus 

 holding it to be identical with xantliopliyll, Pringsheim, on 

 the other hand, regarding it as a different substance. (6) 

 Temperature of a certain degree, the limits varying in in- 

 dividual cases. Both inorganic and organic substances 

 are required for the composition of the colouring 

 matter. Amongst the former iron is important. The 

 various organic matters, both nitrogenous and non-nitro- 

 genous, formed in or taken into the plant supply the chief 

 material for the chlorophyll, and their application to this 

 purpose, and the time and place relations of the formation 

 of the chlorophyll, has been the subject of great contro- 

 versy and much speculation, being intimately bound up 

 with the question of the function of the whole chlorophyll 

 apparatus. In like manner, the formation of the various 



