72 M. Pringsheim on the Action of Light 



general experiences on the relations between the gas-exchange 

 of plants, light, and the function of chlorophyll. 



I reserve the critical estimation of the bearing of the 

 results here communicated of my observations upon the older 

 statements and notions for the full description which is to 

 appear in one of the next numbers of my ' Jahrbucher ftir 

 wissenschaftliche Botanik,' where the necessary figures for 

 illustration will be given. But I will here briefly epitomize 

 the most important points of view for a preliminary eluci- 

 dation. 



T. As regards chlorophyll, the possibility of its destruction 

 by light, in the living plant, is unequivocally demonstrated ; 

 but at the same time it is shown that the destruction is not a 

 normal, but a pathological process. The plant cannot rege- 

 nerate the destroyed colouring-matter ; and the destruction 

 itself is independent of the absorption of C0 2 ; hence it cannot 

 play any part in the assimilation of carbon. 



This overthroAvs every chemical theory that would indicate 

 a genetic origin of the hydrates of carbon from chlorophyll. 



It is further made evident that the destruction takes place 

 in rays of all colours — in the red, yellow, green, and blue ; 

 and it is shown that no definite relation exists between the 

 maxima of light-absorption in the chlorophyll colouring- 

 matter and the colour which originates the destruction. 



II. As regards respiration, not only is the proof produced 

 (which, in full rigour, has hitherto been wanting) that the 

 absorption of oxygen takes place also in direct sunlight — a 

 proposition which strictly was previously only a theoretical 

 postulate, — but it is at the same time shown that respiration 

 is uncommonly heightened when the intensity of the light is 

 increased. It is therefore a simple consequence, as also the 

 directly proved result of my experiments, that the chlorophyll 

 colouring-matter, by its strong absorption of light, lowers the 

 amount of respiration, as it suspends the operation of the 

 photochemically most operative portion of the radiation. 

 Further the materials are discriminated which are used up in 

 the respiration of the plant-cell ; and a series of well-known 

 form-constituents of it are shown to have no part in this. 



III. For the deeper insight into the process of assimilation, 

 by the proof of the presence in all chlorophyll-bodies of a 

 previously unknown body, from which proceeds the starch 

 enclosed in them, the universal primary product of assimila- 

 tion of green plants is discovered. It is already, from the 

 microchemical and morphological properties of this body, 

 rendered in the highest degree probable that it is either a pure 

 hydrocarbon, or else belongs to the series of organic plant- 



