CHROMATIC TRANSIENTS IN RED ALGAE 447 



Figures 3 and 4 are actual photographs of Speedomax records, 

 showing the extremely sharp initial cusp in green, yellow or orange 

 light and the very large depression immediately following. This is 

 especially marked at 560 mju (Fig. 3). There is ne\er a cusp in red 

 light — only the depression followed by recovery. The characteristic 

 time courses are foiuid only when the wavelength of illumination is 

 changed, not the intensity. They are not dependent upon exactly 

 equal steady states; the se\"eral components are present (Fig. 4) 

 at 600 m/x at a higher steady state, or at 560 (lower than red light). 

 They can also be evoked on going from green to yellow light, or vice 

 versa (between the absorption regions of phycoerythrin and phy- 

 cocyanin). They seem indeed to be characteristic of the phycobilin 



Fig. 4. Speedomax record of photosynthetic transient on changing wavelength 

 from red (675 mu) to orange (600 m/i) and back to red (675 m^u) of equal intensity. 

 Time marks 100 seconds. Base line well below the record. 



pigments: no trace of these transients has been seen in green or hrowri 

 algae on alternating light exposures between chlorophyll and carote- 

 noid absorption regions. 



The explanation for these transients is not fully apparent. They 

 are not large compared to some of the effects following long darkness, 

 amounting only to some 10% or 15% of the total oxygen evolution 

 level. They are, however, remarkably consistent and reproducible 

 amongst the algae well-adapted to show them (monostromatous forms 

 with a minimum of diffusion distance to electrode). They have been 

 most conspicuous in three species of Porphyra. Higher red algae — 

 even where monostromatous — do not show them as well. Since 

 Porphyra is the genus in which activation of chlorophyll by red 

 light is also possible (4), it may be that the same mechanism is in- 

 \'olved. Thus even during a short exposure to red light there is par- 

 tial recovery after the lowered initial rate; and conversely an initiallj^ 

 higher rate in green light (due to this recovery?) is followed by a 



