348 The Philippine Journal of Science i»» 



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. 



f . ' V * n Amstel, J - E ' 0n the influence of temperature on the CCVassimila- 

 tion of Helodea canadensis, Rec. Trav. Bot. Neerl. 13 (1916) 1-29. 



