700 



William Arnold and J. B. Davidson 



The phosphoroscope and the fast shutter were arranged so that fluorescence 

 as well as delayed light could be measured. The delayed light signals are 

 plotted in the figure as fractions of the steady state fluorescence signal, 

 which is taken to be unity. The points at 0.6 milliseconds and longer times 

 were taken with the phosphoroscope. The points for the shorter times were 

 made with the Mylar film shutter. The solid curve plotted at the left for 

 reference is an exponential having a time constant of 1.7 X 10~' seconds, 

 which is the lifetime for the fluorescence of Chlorella as given by Tomita 

 and Rabinowitch. 



From Figure 2 it can be seen that intensity of the delayed light at 

 5 X 10"5 seconds is approximately one percent of the fluorescent intensity. 



Extrapolation of the decay curve to even shorter times suggests that a 

 large fraction of the in vivo fluorescence of green plants may actually be 

 delayed light. 



