Carbon Assimilation. 
187 
(1804) who first attempted to obtain quantitative data as to the 
relation between the amount of oxygen evolved and the carbon- 
dioxide absorbed by the assimilating plant. 
Saussure found that the volume of oxygen evolved in a given 
time by the plant was less than the volume of carbon dioxide 
absorbed, and he came to the conclusion that part of the oxygen 
of the carbon dioxide was used in assimilation. It is strange that 
Saussure should be so often quoted as the discoverer of the fact 
that the volume of oxygen given out by the assimilating plant is equal 
to the carbon dioxide absorbed. Thus even Sachs (1882 or see 1887) 
says “As an essential point, it is at the same time to be insisted 
upon here that the volume of oxygen evolved is equal to the volume 
of the carbon dioxide taken in, as de Saussure and, later and more 
exactly, Boussingault have already established.” It is therefore 
worth while to quote Saussure’s conclusion in his own words, “ II 
rdsulte de toutes ces experiences, que les plantes, en ddcomposant 
le gaz acide carbonique, s’assimilent une partie du gaz oxygbne qui 
y est contenu.” 
As Saussure’s work is perhaps not always easily accessible, it 
may be worth while to give his actual results here. 
Saussure placed a suitable number of plants in a large vessel 
containing an artificial atmosphere comprising about 21% oxygen 
and the rest nitrogen, to which was then added carbon dioxide. 
The plants were then exposed to sunlight on a number of successive 
days (6 to 18) and at the end of the period the gas in the vessel 
was analysed. 
The following numbers were obtained with 7 plants of periwinkle 
(Vinca minor). 
Before. 
After. 
Nitrogen 
4199 c.c. 
... 4338 c.c. 
Oxygen 
1116 „ 
1408 „ 
Carbon dioxide 
431 „ 
• • • ^ J) 
5746 
5746 
Oxygen evolved 
• • • • • • 
292 c.c. 
Carbon dioxide absorbed 
431 „ 
Oxygen absorbed by plant 
139 „ 
In the following table are summarised all Saussure’s experi¬ 
ments on this subject. 
