LIISTEAR RANGE 979 



centimeter. For relationships between iV/,^ and intensity of illumination see chapter 25, 

 page 838. 



Table 28.1 does not list the measurements of light curves in the presence 

 of various poisons, such as potassium cyanide, hydroxylamine or azide, 

 of narcotics, such as urethan, or of salts, such as copper sulfate. Several 

 curves of this type are, however, reproduced in figures 28.9-11; for addi- 

 tional information, we refer to chapters 12 and 13 in volume I, and to 

 chapter 37. In the latter, we will also describe the light curves of algae in 

 the state of (almost complete) anaerobic inhibition, which Franck, Prings- 

 heim and Lad (1945) were able to measure by the very sensitive phos- 

 phorescence method. 



Figures 28.1-28.13 contain a selection of typical light curves. Attempt 

 was made to include curves for all types of plants — higher land plants, 

 aquatic higher plants, green and colored algae, diatoms and purple bacteria. 

 Figures 28. 1-28. 5A represent families of curves in which the carbon dioxide 

 concentration, [CO2], serves as parameter (strangely enough, no such set is 

 available for Chlorella). Figure 28. 5B shows light curves of purple bac- 

 teria for two concentrations of the reductant (thiosulfate) ; figures 28.6- 

 28.8 represent curve sets with temperature as parameter. Figures 28.9- 

 28. 1 1 illustrate the effect of inhibitors. The effect of pH (in purple bacteria) 

 is shown in figure 28.12, while figure 28.13 shows the influence of age. 

 Later in this chapter, some additional sets of curves will be given to illus- 

 trate the influence of inherited or acquired conditioning to strong or weak 

 light. 



In chapter 26 we discussed three types of curve sets, P = f[Fi] with a 

 parameter F2, which can be anticipated in photosynthesis. Examples of 

 conditions under which each type can occur were given, for carbon dioxide 

 curves, Fi = [CO2], in chapter 27. 



2. Linear Range 



We will now consider some of the details of the light curves : the linear 

 range, the compensation point, the saturating light intensity and the maxi- 

 mum yield. Perhaps the most important quantitative characteristic of the 

 light curves is the initial slope, which determines the maximum quantum 

 yield; it will be discussed separately in chapter 29. 



Figures 28.1,28.7, 28.9A,28.10and 28.14A,B show that many lightcurves 

 exhibit a practically exact proportionality between rate and light intensity 

 over a considerable range of intensities. This "linear range" is less clearly 

 delimited in figures 28.2-28.6. In the light curves of purple bacteria, it is 

 often obscured by an inflection (c/. figs. 28.8 and 28.11A-D). Data col- 

 lected in Table 28.11 indicate that (at room temperature and with an ample 



