C. S. I'RENCH 



449 



lengths than in ether sohition. The bhie absorption bands of chloro- 

 phyll are largely obscured by carotenoid absorption and the 615, 578, 

 and 535 bands are small. The spectroscopic study of chlorophyll 

 a in live plants is therefore mainly restricted to the major red ab- 

 sorption band. The shape of this band has been investigated in many 

 different algae and found to be a composite of several individual 

 components (26). 



The purple bacteria show various forms of the complexed bac- 

 teriochlorophyll with great clarity, since the bands are more widely 

 spaced than in green plants (13, 19, 36, 57, 58). Duysens (13) 

 designates the forms of bacteriochlorophyll in vivo as B800, B860, 

 B870, B890, etc., according to the wavelength of the main absorption 

 peak of each type. We use this notation to distinguish the various 

 forms of chlorophyll a and b and protochlorophyll in plants as 

 C,650, C„673, Q695, P^s^, Pe.o, etc. 



The chemical nature of the natural chlorophyll complex (holo- 

 chrome) is not known. In green plants chlorophyll a is present in 

 several different forms, like the bacteriochlorophyll in photosynthetic 

 bacteria, but the bands in green plants are much closer together. 

 Chlorophyll a, instantly after its formation in leaves from proto- 

 chlorophyll, absorbs at 682 m^u,. (53, 54) , as seen in Fig. 1 (fluores- 

 cence peak 691 m^, Latimer, 44) . After a few minutes of illumina- 



0.4 



"Z 0.3 



e 



0.2 



> 



0. 



n 1 — r 



Chl-670,'- 



Chl-682 



J L 



550 600 650 700 



Wavelength m^ 



Fig. 1. Two kinds of chlorophyll a in a bean leaf. The dashed curve, Pchl, is 

 the absorption spectrum of protochlorophyll in a bean leaf grown in the dark. 

 The full line, Chi 082, is the absorption of the freshly formed chlorophyll a im- 

 mediately after exposure to light. The dotted curve. Chi 670, shows the spectrum 

 after the same leaf had been 30 niin. in the dark following illumination. From 

 J. H. C. Smith (54). 



