NO. 



l6 CARBON DIOXIDE ASSIMILATION HOOVER ET AL. I5 



respiration measurements involve changes in concentration which 

 are small compared to those of assimilation measurements. This 

 accounts for the fact that whereas our error of observation is suffi- 

 cient to account for the difference between these growth curves, it 

 it still small when considered on the scale of the assimilation curves. 

 The method of growth correction adopted in the second experiment 

 being based upon assimilation under identical conditions has an 

 accuracy of the same order as the assimilation measurements them- 

 selves. Thus the arbitrary factor involved in the interpretation of 

 the first experiment is wholly eliminated in the second. 



The first set of curves are interesting, however, first, because they 

 show observations made over a wider range of light intensities, and, 

 second, because although made in a completely dift'erent order of 

 sequences in time, they are in complete agreement. If any marked 

 effects of day and night or age were present, such agreement would 

 not be possible even through arbitrary growth correction. 



In order to further compare the results of the first experiment 

 with those of the second, curves have been derived from the corrected 

 data (fig. 4) showing carbon dioxide assimilation as a function of 

 carbon dioxide concentration with light intensities as parameters. 

 These are shown in Figure 6. 



Directly from the second experiment we obtain assimilation rate 

 as a function of carbon dioxide concentration for six light intensities 

 as given in Figure 7. In the main points the two experiments are 

 in reasonably good agreement, remembering of course that dift"erent 

 plants have been used so that the assimilation values are not directly 

 comparable. For the highest light intensity, 191 (fig. 7), we see 

 that the assimilation rate is proportional to the carbon dioxide con- 

 centration from o to about 850. The maximum rate is not reached 

 until the concentration has been increased to about 3,500. A further 

 increase in the concentration produces no change in the assimilation 

 rate. As the light intensity is decreased the departure from the linear 

 relation occurs at a lower and lower carbon dioxide concentration. 

 The maximum assimilation rate is less and the maximum is reached 

 at a lower carbon dioxide concentration. In Figure 8 we see, for a 

 carbon dioxide concentration of 3.500 or more, that the assimilation 

 rate is proportional to the light intensity from o to the highest in- 

 tensity used. As the concentration is decreased the departure from 

 the linear relation occurs at a lower and lower light intensity. For 

 small carbon dioxide concentrations a maximum rate of photo- 

 synthesis is reached for the light intensities used in this experiment. 

 A further increase in intensity produces no change in the assimilation 



