SPECTRAL PROPERTIES OF CELLULAR PIGMENTS 



31 



100 



50 



PCRIDINIUM 

 GONYAULAX 



400 SCO iOO 700 



WAVEllNGTN IN m^l 



Fig. 10. Phototaxis action spectra. 



need for better methods of detecting minor pigment components in 

 absorption spectra. 



DERIVATIVE SPECTROPHOTOMETRY 



We have recently completed a device for recording the slope of an 

 absorption curve rather than its height. This machine plots the first 

 derivative of optical density against wavelength. The method is ex- 

 pected to be useful for detecting minor bands which are obscured by 

 more strongly absorbing pigments (Giese and French, 1955). The 

 type of measurement given by this device is shown in Fig. 11 from 

 French (1957). On the left is plotted the absorption of chlorophyll a 

 in ether solution as measured by the Beckman recording spectro- 

 photometer. On the upper right we see the first derivative of optical 

 density, dE/d\, plotted against wavelength A, by the new machine. 

 The integral of this plot is drawn as the full line on the upper left for 



