138 



J. E. imUGGER 



before irradiation, caused the chemiluminescence to increase. The 

 luminescence measured in the presence of carbon dioxide and nitrogen 

 (no oxygen) was slightly greater than that measured with carbon 

 dioxide and air present. 



Figure 5 shows the effect of a change to pure oxygen following 

 irradiation under pure nitrogen. Similarly, it was observed that the 

 chemiluminescence was higher in the presence of ordinary tank ni- 

 trogen than in the presence of our specially purified gas. 



18 



16 



<^ 14 



UJ 



o 12 — 



10^ 



8r 



I 



6^ 



UJ 



2 







L 



SCENEDESMUS 



N2 -NUTRIENT 



A = I0"2 M PHENYLURETHANE 

 B=NO PHENYLURETHANE 







I 2 3 4 5 6 



IRRADIATION (MINUTES) 



Fig. 6. Time course of delaj^ed luminescence during irradiation of Scenedesmua 

 in nutrient solution. Nitrogen atmosphere. Effect of A'^-phenylurethane. 



The conclusion that the chemiluminescence is least intense when 

 photosynthesis is proceeding with great facility is bolstered by studies 

 made with various poisons, inhibitors, and narcotics. A curve made 

 using Scenedesmus to which A^-phenylurethane had been added is 

 sho\vn in Fig. 6. 



The intensity of the chemiluminescence in the steady state is 

 roughly linear with irradiation intensity under the conditions of our 

 experiments. (We normally operated in the region of near saturating 

 intensities.) This is to be contrasted with the finding of Arnold that 

 the luminescence saturates at low intensities of irradiation. Whether 

 one observes a saturation or a linear rise with increasing irradiation 

 depends on the time delay between irradiation and measurement of 

 the luminescence. In our experiments, the time elapsed is less than a 

 millisecond, whereas in those of Strehler and Arnold it is of the order 

 of tenths of seconds. 



I shall not discuss these experimental results and observations in 



