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The Philippine Journal of Science 
1918 
very clearly by the form of the curve. It would seem, however, 
that it would be more instructive to draw separate curves for 
the experiments with different light intensities. Following this 
idea a solid line has been drawn to represent the experiments 
performed with 5.7 units of light, and a line of short dashes 
to represent those with 8.1 units. On examining these two 
curves it will be seen that the curve for 8.1 units of light is 
considerably higher than that for 5.7 units, a result which is 
not surprising. The curve for 8.1 units does not appear to 
reach an optimum with the supply of carbon dioxide employed 
with this light. The curve for 5.7 units at first rises rapidly 
with increasing concentrations of carbon dioxide, then more 
slowly until it reaches what appears to be an optimum, after 
which it falls. An examination of the two experiments with the 
highest concentrations shows that they were performed at tem- 
peratures of 28° and 30°, whereas those with the lower concen- 
trations were carried out with a temperature of 19°. According 
to the work of Van Amstel, 7 a rise of temperature from 24° to 
34° increases the rate of assimilation of Elodea by 26 per cent. 
Now, in view of this, it seems possible that these last two ex- 
periments showed a rate of assimilation at least 20 per cent 
higher than they would have shown had they been performed 
at a temperature of 19°. If we apply to them a correction of 
20 per cent, then the points representing them would take the 
positions indicted by the broken circles. The curve drawn to 
pass between these points is shown as a dotted line and indi- 
cates, even more clearly than the solid line, that there is an 
optimum concentration of carbon dioxide. Either the curve 
represented by the solid line, or this curve as modified by the 
dotted line, would seem to represent the experiments more ac- 
curately than Blackman and Smith’s curve, and both fail to 
show the operation of any limiting factor. Moreover, since the 
curve for light intensity of 5.7 units rises with increasing con- 
centration of carbon dioxide up to a certain point, and the 
curve for light intensity of 8.1 lies above it, it would seem 
that an increase in either the light intensity or the carbon 
dioxide would bring about an increased rate of assimilation. 
This is, of course, exactly the opposite of Blackman’s theory, 
according to which it would be impossible to increase the in- 
tensity of either one of two factors and in either case get an 
increase in the rate of the process. 
1 Van Amstel, J. E., On the influence of temperature on the COu-assimila- 
tion of Helodea canadensis, Rec. Trav. Bot. Neerl. 13 (1916) 1-29. 
