12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/ 



The data, without correction for growth, are plotted in Figure 3. 

 An extrapolation of the curves in this figure indicate a small apparent 

 assimilation rate for zero light intensity. This may be explained by 

 a leakage of carbon dioxide into the apparatus through the rubber 

 tubing which constituted part of the air line in this first experiment. 

 This trouble was eliminated in later experiments by making a prac- 

 tically all-vitreous air system. 



We had hoped to determine the growth curve of the plants from 

 respiration measurements, but the changes in concentration of carbon 

 dioxide in the air due to respiration proved to be too small to give 

 accurate results. An approximate curve was obtained from the daily 

 measurements of leaf lengths. The interpretation of these curves 

 will be discussed in connection with the second experiment. 



SFXOND EXPERIMENT 



In this experiment the order of procedure was reversed. The 

 light intensity was held constant and the assimilation rate on a given 

 day determined for several different carbon dioxide concentrations. 

 This was repeated for five other light intensities. The data for this 

 series of experiments are given in Table 2 and Figures 7 and 8. 

 Thus we obtain immediately curves showing the assimilation rate 

 as a function of the carbon dioxide concentration for six light in- 

 tensities (fig. 7). The data for Figure 8 are derived from Figure 7. 

 The curves in this figure show the assimilation rate as a function 

 of the light intensity for several concentrations of carbon dioxide. 



In the second experiment the rubber connections were eliminated 

 by construction of a practically all-vitreous system. The growth 

 curve for this experiment was determined in a manner somewhat 

 similar to that employed by Van den Honert. The assimilation rate 

 of the plants was measured under the same conditions, twice each 

 day, and a linear growth relation assumed for the intervening time. 



DISCUSSION OF RESULTS 



In order to compare the curves of the first experiment with those 

 of the second experiment growth correction must be applied to the 

 data of Figure 3. Applying arbitrary growth factors which will bring 

 the two sets of curves into harmony after making the zero correction 

 for leakage, we obtain Figure 4. These arbitrary growth factors are 

 plotted in Figure 5 and are shown by the solid curve. It is interesting 

 to compare this curve with the curve for total leaf length indicated 

 by the dotted line and those obtained from the respiration measure- 

 ments shown by the broken line. It must be borne in mind that the 



