188 Ingvar Jorgensen and Walter Stiles. 
Table XXIV. 
Oxygen evolved in Assimilation (de Saussure). 
Species. 
Oxygen evolved. 
C0 2 absorbed. 
Oxygen 
absorbed. 
Vinca minor . 
292 c.c. 
431 c.c.. 
139 c.c. 
Mentha aquatica 
224 „ 
309 „ 
86 „ 
Lythrum salicaria 
121 „ 
149 „ 
27 „ 
Pinus genevensis 
246 „ 
306 ,, 
60 „ 
Cactus opuntia. 
126 „ 
184 „ 
57 „ 
Such experiments as these, of course, take no account of the 
respiration of the plants which is certainly going on in the intervals 
between the illuminated periods and is generally assumed to 
continue concurrently with assimilation during the illuminated 
periods as well. The same criticism is to he 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 °^^ en ratio considerably greater than unity (1-05 
to 1 *33). Similar numbers were also obtained for lichens by 
Jumelle (1892), and for mosses by Jonsson (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 
CO c' 
The respiratory coefficient =— = r. 
o 
Similarly if in the same time 
o is the oxygen evolved in the light and 
c „ „ carbon dioxide absorbed in the light 
