86 The Philippine Journal of Science lei? 
There are progressively greater deviations from the Bunsen- 
Roscoe law with still higher light intensities. The augmentation 
of photographic effect proceeds more and more slowly until there 
is no further increase, when a certain limiting light intensity is 
reached. 
The photosynthetic assimilation of carbon dioxide by plants 
is a complicated reaction affected by many factors; hence there 
is a priori no reason to expect that the relationship between 
assimilation and light intensity under natural conditions should 
be expressed as a simple, direct proportionality. The general 
statements ^ in the literature, however, give the impression that 
the amount of carbon dioxide assimilation in plants is directly 
proportional to the intensity of the incident light. The writers 
have recently had occasion to review the literature on photo- 
synthesis, and believe it worth while to call attention to the fact 
that these statements by no means express the conclusions to be 
' PfeflFer(i'?> says: 
The photosynthetic activity increases proportionately to the intensity of 
the light, as has been repeatedly shown since the first experiments by 
Wolkoff. There is, however, a limit to the increase. 
Further on, the foregoing statement is somewhat amended as follows: 
No mathematically exact relation can be expected between the photosyn- 
thetic activity and the intensity of the light, for as the light increases 
other influences maj'^ be exerted, which directly or indirectly modify the 
assimilatory powers of the chloroplastids. 
According to Jost(io) : 
As the light increases in intensity, COj-assimilation also increases. 
When the light is about as intense as ordinary sunlight, however, this 
relation is not maintained, and this for several reasons. 
Barnes (1) writes: 
From the point at which the effective energy of the light absorbed is 
just equal to disposing of the available CO 2 , whether this is greater than 
natural or not, lessening the intensity of the light results in a propor- 
tional diminution of the amount of the product. 
Blackman and Matthaei<2) make the following statement: 
The general views expressed in this paper involve the assumption that 
with all intensities of light the amount of assimilation is proportional to 
the intensity of the light unless some secondary or limiting factor is at 
work. 
Blackman and Smith (3) in their work on Elodea determined two points 
on a curve representing the relation between carbon dioxide assimilation 
and light intensity and then drew the curve as a straight line. 
Jorgensen and Stiles O) in an extensive review of the recent literature 
on carbon dioxide assimilation also hold that assimilation is directly pro- 
portional to light intensity. 
