382 



Max H. Homme r sand 



I 



480nfUi 



5 25mu 



650 mu 



eSOmp 



720 m>j 



Fig. 1. Oxygen transients measured at five differ- 

 ent wavelengths. Monochromatic light of 6.6 mja half- 

 band-width was provided from a Bausch & Lomb monochro- 

 mator. The curves are plotted from galvanometer read- 

 ings taken every fifteen seconds. Other details in 

 the text. 



intensities were used which gave the same steady-state photosyn- 

 thesis rate at each wavelength. This was even true of transients 

 measured in the far-red region. Some selected examples are shown 

 in figure 1. The transient at 720mp is particularly interesting 

 because of its similarity to the transients occurring in the 

 visible region. Since oxygen evolution in untreated whole cells 

 probably requires the participation of two pigment systems, it 

 appears that in this strain there is relatively good overlap in 

 absorption by the pigments of the two systems even at relatively 

 long wavelengths. 



The details in the shape of a light-dark oxygen transient are 

 repeatable when a series of such transients are measured at a 

 particular wavelength. If, however, at the end of the period of 

 a transient the wavelength of the light is shifted and the light 

 intensity at the new wavelength is preset to give the same 

 steady-state photosynthesis rate, then a new transient having a 



I 



