Carbon Assimilation. 
189 
Then the total oxygen produced by the assimilatory 
process in the given time is o + o' 
and the total carbon dioxide absorbed in assimilation 
is c + c’ 
And the true assimilatory coefficient is 
0 + 0' O 
q _|_ c 1 Q 
2. The second method employed by Bonnier and Mangin is 
based on Bernard’s observation (1878) that by the use of chloroform 
the assimilation may be suppressed and respiration alone takes 
place. By comparison of the gaseous exchanges taking place in 
two similar quantities of leaves exposed to light under the same 
conditions, hut in which one was anaesthetised with ether, and the 
other not, the gaseous exchange due to assimilation may be 
estimated. 
3. Bonnier and Mangin’s third method is based on the 
suppression of assimilation by removal of all carbon dioxide from the 
neighbourhood of the leaves. Two similar vessels contain equal 
weights of similar leafy tissue; one of the vessels contains 
concentrated barium hydroxide solution, the other an equal volume 
of pure water. In the former, not only is the carbon dioxide 
of the atmosphere removed and assimilation prevented, but the 
carbon dioxide evolved in respiration is absorbed by the baryta. So 
that, as in the second method, the difference between the oxygen 
content and carbon dioxide content of the two vessels at the end 
of the experiment, gives the true values for oxygen and carbon 
dioxide evolved and absorbed respectively in assimilation. 
4. The fourth method depends on the measurement of the 
gaseous exchanges in branches of the same plant which are 
unequally green. Thus a yellow branch of Euonymus japonicus on 
exposure to light evolved 2‘89 units of carbon dioxide and absorbed 
2-11 of oxygen, while in the same time a green branch evolved 2'27 
of oxygen and absorbed 0*54 of carbon dioxide. 
The four different methods gave concordant results. The 
results obtained by Bonnier and Mangin for a number of species at 
different times of the year are shown in Table XXV. It will be 
observed that the true assimilatory coefficient is always greater than 
unity, whereas the respiratory coefficient is below unity. The 
consequence of this is that the apparent assimilatory coefficient, 
which neglects the respiration, is always lower than the real 
