C. STACY FRENCH 



67 



be that the chlorophyll b fluorescence band is near enough to the 

 absorption maximum of chlorophyll a to be strongly reabsorbed. 



The fluorescence spectrum of two suspensions of the diatom 

 Nitschia, kindly given us by Professor C. B. van Niel, which is 

 presumed to contain chlorophyll c, is shown in Fig. 16 as compared 

 with the fluorescence spectrum of the white part of an ivy leaf. 



Nitistliio svspention 



600 



iSO 700 



WAVELENGTH 



7S0in;i 



Fig. 16. Fluorescence spectra of a thick and a tliin suspension of Nitzschia clos- 

 terium, minutissima, as compared with that of clilorophyll a in the white part 

 of a variegated ivy leaf. The diatom culture was kindly gi\ en us by Professor 

 C. B. van Niel. 



Instead of finding a chlorophyll c band at the anticipated position of 

 approximately 640 mix, a new band appeared at about 705 m/x. The 

 cause of this 705-m/ut fluorescence is not known. One possible interpre- 

 tation might be that it is indeed due to chlorophyll c, but it is the 

 longer wavelength subsidiary band which could reasonably be ex- 

 pected to be at about this position and that the absence of the main 

 band, anticipated at about 640 m/x, is due to its reabsorption by 

 chlorophyll a within the diatoms. The cells themselves are quite dark 

 so that very strong reabsorption of fluorescence, even within a single 

 cell, might not be inconceivable. The action spectrum for the excita- 

 tion of fluorescence in this material, Fig. 17. confirms again the 

 participation of hght absorbed by fucoxanthin in the excitation of 



