62 



PHOTOCHEMICAL PRINCIPLES 



clarify this point, and these are in the process of being measured in our 

 laboratory. Similar experiments demonstrate that the low-temperature 

 0.3 -sec emission is excited only by wavelengths between 3500 A and 

 4500 A (light between 6000 A and 7000 A has no effect) and that 

 this emission consists of wavelengths between 10,000 A and 12,000 A. 

 Figure 7 shows the effects of allowing freshly prepared chloroplasts 



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< 

 a: 



m 



< 





8- 

 6-- 



4- 

 3 ■ 



8 

 6 



4- 

 3 



T 1 1 



o FRESHLY PREPARED 

 X 8 HOURS STANDING 

 • 24 HOURS STANDING 

 D 48 HOURS STANDING 



.4 

 TIME 



.6 .8 



(SECONDS) 



1.0 



1.2 



Fig. 7. Effects of allowing freshly prepared wet, whole spinach chloro- 

 plasts to stand in the dark at 23 °C. 



to Stand in the dark at 23 °C. Up to 8 hr, the luminescence gradually 

 increases in intensity and reaches a maximum intensity of 2.7 times 

 that of freshly prepared material. This larger signal exhibits the same 

 decay curve, wavelength properties, and temperature behavior as does 

 the original signal. Allowing the chloroplasts to stand still longer de- 

 creases the luminescence intensity and causes changes in the decay 

 curve. After about 72 hr the luminescence has disappeared entirely, 

 and the chloroplasts will exhibit thermoluminescence similar to that 



