SPECTRAL PROPERTIES OF CELLULAR PIGMENTS 



27 



photometry of the intact leaves, as was done by Shibata (1957b). The 

 absorption peak of protochlorophyll consists of two components with 

 maxima at about 635 and 650 m/x. Upon illumination the maximum 

 at 650 decreases and chlorophyll a is formed with an absorption peak 

 at 682 m/x. After standing in the dark for about 30 min the chlorophyll 

 changes over to another form absorbing at about 670 mju,. The first 

 change from protochlorophyll to C682 is a purely photochemical 

 action which will take place even at the temperature of solid carbon 

 dioxide. 



Light is not necessary for the transformation of C682 to C670. 

 The action spectrum for the photochemical change was determined 

 in corn seedlings by Koski, French, and Smith ( 1951 ) with the appa- 

 ratus shown in Fig. 6. The light from a high-pressure mercury lamp 

 was sent through a monochromator, and an image of the grating was 



OUTLINE OF 

 VERTICAL BEAM 



THERMOPILE 



DARKROOM WALL 



WATER FILTER 



COUPLING GEAR 



WATER COOLED HIGH PRESSURE 

 MERCURY LAMP 



CRANK 



TOP VIEW 



Fig. 6. The monochromator and optical systems used to measure the 

 action spectrum of chlorophyll formation in etiolated corn leaves (Koski, 

 French, and Smith, 1951). 



