1270 



THE PIGMENT FACTOR 



CHAP. 32 



leaves, shown in Table 31.IV; but the reason for this difference may be 

 simply that the aurea leaves were studied in a state of incomplete light 

 saturation (c/. fig. 32.2), while Emerson used Hght intensity sufficient to 

 saturate both the normal and the chlorophyll-deficient Chlorella cells (c/. 

 fig. 32.4). Theoretically, there seems to be no reason why the temperature 

 coefficient of P™^'"' should change with [Chi], at least as long as the same 

 dark reaction is rate-limiting in all the cell systems under comparison. 



The photosynthesis of chlorotic Chlorella cells was found by Emerson to 

 to be more strongly affected by cyanide than that of the normal ones. 

 This may indicate that chlorotic cells contained less of the cyanide-sensi- 

 tive carboxylating enzyme, Ea {cf. Volume I, page 306). 



I I 



Fig. 32.5. Light curves of optically dense (— ) and optically thin (— ) systems: (A) 

 normal and chlorotic Chlorella cells (cf. fig. 32.4); (B) normal and yellow Sarnbucus 

 leaves {cf. fig. 32.2); and (C) shade and sun leaves {cf. fig. 28.10-18). 



Fleischer (1935) repeated Emerson's experiments, varying the chloro- 

 phyll concentration of Chlorella by three types of changes in the nutrient 

 medium: (a) changing the iron concentration, (6) changing the nitrogen 

 concentration and (c) changing the concentrations of magnesium {cf. 

 chapters 13 and 15). Results obtained by the methods a and h, (using 

 Warburg's buffer No. 9, and fight of 75,000 lux) weresimilar; likeEmerson's 

 observations, they showed an approximately linear increase in yield with 

 the chlorophyll concentration. Method c, on the other hand, gave more 

 complex results, indicating that magnesium deficiency had a specific effect 

 on photosynthesis, beside the indirect influence caused by a lowering of 

 chlorophyll concentration. Van Hille (1937), was unable to confirm 

 Fleischer's results; he found a systematic decrease in both [Chi] and P'"*''' 

 in plants deprived of magnesium. However, the existence of a direct ef- 

 fect of magnesium concentration on the rate of photosynthesis was con- 

 firmed by Kennedy (1940) {cf. chapter 13, page 337). 



In a second paper, van Hille (1938) reported that the photosynthetic 

 capacity of Chlorella pyrenoidosa cultures decreased steadily with age, even 

 if the chlorophyll content continued to increase. Experiments with varied 

 nutrient solutions showed that this decline was connected with a develop- 



