and the Function of Chlorophyll in Plants. 73 



constituents which contain less oxygen than the so-called 

 hydrates of carbon. 



This, again, if the most probable hypothesis be admitted, 

 that plants build up their first carbonaceous material out of 

 carbonic acid and water, explains in a natural way why, not- 

 withstanding the exceedingly heightened respiration in light, 

 the volumes of the air-filled closed spaces in which plants 

 are cultivated in sunlight may yet remain unaltered in 

 magnitude. 



IV. The function of the green colour of vegetables is reduced, 

 in a way widely deviating from present notions, to its im- 

 portance for the respiration of oxygen. It is shown that 

 chlorophyll, as the regulator of the plant's respiration in light, 

 by its strong absorption of the chemically most operative 

 rays, depresses the amount of the respiration of green plants 

 below that of their assimilation, and thus renders possible the 

 accumulation of carbon-containing products and the existence 

 of the plant in light. 



This extinction of the blue rays in chlorophyll at the same 

 time accounts for the observed greater efficiency of the rays of 

 medium refrangibility for the evolution of the oxygen of the 

 plant, as well as for the apparent coincidence of the assimila- 

 tion-curve of the plant with the brightness-curve of the 

 human eye. Unquestionably the maximum of assimilation 

 for different plants lies in different parts of the effective rays 

 of medium refrangibility, and depends on the amount of ex- 

 tinction (absolutely different for different plants) of the 

 chemical rays in the chlorophyll. 



Is this function of limiting the respiration the only one 

 which chlorophyll exercises in the gas-exchange of plants ? 

 I shall return to this question in subsequent papers. It is 

 indubitable that at present it is the only one actually demon- 

 strated ; for the sole support which, since the discovery of the 

 giving-out of oxygen by plants, has hitherto always again 

 and again been urged for the direct participation of chlorophyll 

 in the process of decomposing carbonic acid, namely that only 

 green parts liberate oxygen, finds in the lowering of the 

 amount of the respiration by the chlorophyll its sufficient 

 explanation. 



V. In conclusion, it must be mentioned that for a series of 

 plant-constituents belonging to the class of ethereal oils and 

 their immediate derivates, and which it has been customary 

 to explain as exclusively products of a reti-ograde metamor- 

 phosis, a universal immediate origin within the elementary 

 substance of every chlorophyll-grain is demonstrated' — a 

 further following-out of which promises important elucida- 



