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xu, c,1 Brown and Heise: Carbon Dioxide Assimilation 11 
The rate of assimilation is much less than in the former ex- 
periments with the same intensity of light. This difference is — 
emphasized by Matthaei and apparently is due to the time of the 
year, the former experiments having been performed much 
earlier, as will be seen from-the dates given in the tables. 
The column for light intensity of two units shows a higher 
rate of assimilation than that for one unit. There is, however, 
no difference in the rate for different temperatures above 0.4°. 
The results with light intensity of four units are not so clear. 
The two determinations at 11.4° and the one at 24.8° are very 
similar, being respectively .00465 and .00485. The figure for 
25.2° is .00615. Evidently there must be a considerable experi- 
mental error either in the result for 24.8° or for 25.2°, as a rise 
of 0.4° can hardly account for the difference in the results. 
Matthaei discards the figure for 24.8° because (footnote p. 27) 
the results in experiment 36 for light intensities of one and four 
units “are far too small in comparison with the other experi- 
ments.” However, the results for one unit are well within the 
limits of experimental error indicated in Table I. The rates of 
assimilation for temperatures of 9.2° and 11.4° are also very 
different. It will be seen that the figure for light intensity of 
four units at 9.2° is less than for light intensity of two units 
at 8.8°. The results for light intensity of four units are plotted 
in fig. 2. The form of the curve seems to show that the results 
are such that no reliable conclusions can be drawn from them. 
If the figures for 11.4° and 24.8° are correct, there is very little 
or no rise in the rate of assimilation; if the results for 9.2° and 
25.2° are reliable, there is a considerable rise. As the measure- 
ments of light were not exact, it is possible that the irregularities 
in the results are due to differences in the intensity of light. 
It will be noted that experiments 13 and 14 (Table 1) at 14.2° 
and 14.0° with unit light intensity show very different results. 
In this case, however, there are enough other experiments to 
show that the results are due to experimental error. 
The discussion of the results with light intensities of four units 
is important, because it is by them that Matthaei attempts to 
prove that light was not a limiting factor in obtaining her result 
for assimilation at a temperature of 9°. The figures for light 
intensity of four units should be judged by their relation to the 
general results. In no other case will it be necessary to call into 
question the reliability of any figure to show that Matthaei did 
not eliminate the probability of light being a controlling factor 
at any temperature between 3° and 33°. 
There were two determinations of assimilation with light in- 
