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1917 
shown that this method must be used with great caution and that 
consequently the published data are to a large extent unreliable. 
For example, Kniep found that the oxygen content of the 
bubbles varied from 22 to 45 per cent, depending upon the 
intensity of the incident light. His paper makes it very clear 
that the number of bubbles given off by a plant on illumination 
is not necessarily proportional to the assimilation. 
SUMMARY 
The published work on photosynthesis does not warrant the 
generally accepted conclusion that carbon dioxide assimilation in 
plants is proportional to the light intensity. Instead they in- 
dicate a progressively smaller augmentation of the rate of assi- 
milation for each increase in light intensity. This decrease in 
the rate of augmentation continues until a point is reached at 
which further increase in light produces no measurable increase 
in assimilation. 
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