1234 THE TEMPERATURE FACTOR CHAP. 31 



clined to unity at / = 1. Figure 31.9 shows similar results obtained more 

 recently by Emerson and Green (1934) with the red alga Gigartina; here 

 the rate obtained at the lower light intensities (and with an ample supply of 

 carbon dioxide) is practically independent of temperature between 4° and 

 16° C. Emerson and Lewis (1940, 1941) in their work on the maximum 

 quantum yield, 70, of photosynthesis in Chlorella (cf. chapter 29) found no 

 significant differences between the 70 values at 0°, 10° and 20° C. Similar 

 results were obtained by Wassink, Vermeulen, Reman and Katz (1938) 

 and Noddack and Kopp (1940), (c/. figs. 28.6 and 28.7). 



Figure 28.7A refers to experiments in white light, and figure 28.7B, to those in 

 monochromatic (red) light. It will be remembered (c/. page 1160) that Noddack and 

 Eichhoff found that the "light curves" bend early in white light, but remain linear until 

 close to saturation in red light. The difference between figures 28.7A and B corresponds 

 to these findings. In the first case, the rate is independent of temperature only in ex- 

 tremely weak light, whereas, in the second one, the light curves corresponding to 10° 

 and 20° C. (corrected for respiration) coincide over a considerable range of light inten- 

 sities. We said (pp. 1098 and 1162) that the origin of differences between the shapes of 

 light curves in white and red light, claimed by Noddack and co-workers, is obscure; 

 here we must be satisfied with the fact that, whether the light curves bend early or late, 

 the rate is independent of temperature so long (and only so long) as they are linear. 

 In other words, temperature dependence becomes evident as soon as some dark process 

 interferes to reduce the over-all rate below the maximum value allowed by the primary 

 photochemical process. 



Table 31.III 

 Compensation Point and Temperatube 



Observer Organism 



le (in lux) 



Ehrke (1931) Entheromorpha compressa 



Fucus serratus 

 Plocamium coccineum 



Muller (1938) Salix glauca 



Chamaenerium latifolium 



Of course, the rate can be independent of temperature only within the 

 "biokinetic" range. The drop in efficiency at the two ends of this range 

 cannot be avoided, however weak the illumination. Blackman and Mat- 

 thaei (1905) found that the rate of photosynthesis of cherry laurel leaves 

 declines sharply below 0° C, in weak as well as in strong light. There 

 appear to be no data available on the rate of photosynthesis in weak light 

 at temperatures above 30° ; but one can expect that, sooner or later, super- 

 optimal temperatures will affect photosynthesis also in the hght-limited 

 state. However, if the exceptional sensitivity of photosynthesis to heat is 

 due mainly, or partly, to the enzyme that limits the rate in strong fight, 

 the quantum yield in weak light may remain unimpaired, at least for some 



