98 Carbon Assimilation. 



Tabli-: XXIV. 



Oxygen evolved In Assiinihitioii (tie Saussure). 



Such experiments as these, of course, take no account of the 

 respiration of the plants which is certainly going on in the intervals 

 hetween the illuminated periods and is generally assumed to 

 continue concurrently with assimilation during the illuminated 

 periods as well. The same criticism is to be levelled against the 

 experiments of Boussingault (1864) and others, who obtained a ratio 

 of oxygen evolved to carbon dioxide taken in, of approximately 

 unity, and to those of Schloessing (1892, 1893), who obtained 



numbers for the -^J^ — ratio considerably greater than unity (1-05 



to 1'33). Similar numbers were also obtained for lichens by 

 Jumelle (1892), and for mosses by Jijnsson (1894). 



It was Bonnier and Mangin (1886) who attempted to separate 

 the gaseous exchanges due to assimilation and respiration. For 

 this purpose they employed four different methods. 



1 . By successive exposure of the same green tissue to darkness 

 and light in a closed vessel and measurement of the change in 

 content of oxygen and carbon dioxide of the vessel in which the 

 tissue is enclosed during each period, it is possible to obtain data 

 for the gaseous exchange due to assimilation alone. 



Thus if in any time 



c' is the carbon dioxide evolved in the dark and 

 o' „ „ oxygen absorbed in the dark 



The respiratory coefficient —^ == S_ = r. 



O2 o' 



Similarly if in the same time 



o is the oxygen evolved in the light and 



c „ „ carbon dioxide absorbed in the light 



