466 



S. S. Brody and M. Brody 



/ > , 



OCHROMONAS DANICA 

 2 DAYS 



N, TEMP. 

 ROOM TEMP. 



450 500 550 600 650 700 750 



WAVELENGTH, mu 



Fig. 8 Fluorescence spectra excited 

 at 436 m)i. 



450 500 550 600 650 700 750 



WAVELENGTH, m/i 



Fig. 9 Fluorescence spectra excited 

 at 436 m(jL. 



at shorter wavelengths is displaced about 3 m|jL, the one at longer wavelengths 

 about 24 mjjL from the maximum of the fluorescence band obtained at room 

 temperature. (Freed and Sancier (26) have shown that a shift in absorption 

 toward longer wavelengths should be expected upon cooling. ) We w^ill refer 

 to the former as the monomer band, since it corresponds in position with the 

 fluorescence band obtained with dilute solutions of chlorophyll; the latter will 

 be designated the aggregate band, since it corresponds in position with the 

 fluorescence obtained with concentrated solutions of chlorophyll. ( 4 ) 



Measurements made at the temperature of liquid nitrogen also show (Figs. 

 7, 8 and 9) a shift in band maxima with ageing. 



It can be clearly seen that in young Ochromonas the intensity of fluores- 

 cence from the monomer is greater than from the dimer; with age, both 

 increase, but fluorescence from the aggregate increases at a faster rate. 

 By 10 days the intensities of emission from the monomer and aggregate are 

 about equal. This situation is also characteristic of higher plants, in which 

 the intensity of emission from both bands is about equal in mature leaves 

 during the entire growing season. (See Figs. 11 and 12). 



The fluorescence properties of Chlorella are similar to those of 

 Ochromonas and higher plants. However, as mentioned above, Ochromonas 

 has only chlorophyll a; higher plants have in addition, chlorophyll b. 

 Chlorella may be considered an extreme "shade" plant since it has a high 

 proportion of chlorophyll b. In Fig. 4 it may be seen that in addition to the 



