CHLOROPHYLL BANDS IN PLANTS 



697 



Two characteristics strike the eye in all the above-reproduced curves; 

 the shift of band maxima toward longer waves (as compared with their 

 position in solution spectra) , and the diffuse appearance of all bands, leading 

 to considerable absorption (or apparent absorption) in those regions (green 

 and extreme red) where pigment solutions are almost completely trans- 

 parent. Of these two characteristics, the first one can be safely attributed 

 to changes in the intrinsic absorption curves of the pigments in the cell (cf. 

 page 698). The shapes of the bands, on the other hand, are affected 

 largely, but probably not exclusively, by scattering, "sieve effect," and 

 other phenomena of geometrical optics. 



40 



35- 



Young 



J_ 



_!_ 



40 

 35 

 30 

 25 

 20 

 15 

 10 

 5 



430 460 500 540 580 620 660 700 400 450 500 550 600 650 700 



WAVE LENGTH, m/i 



Fig. 22.32. Reflection (/?//) of leaves of 

 Tilia americana (after Shull 1929). 



WAVE LENGTH, rufi 



Fig. 22.33. Average reflection from 

 green and fall-colored leaves (after 

 Loomis, Carr and Randall 1941). 20- 

 80 species averaged for each curve. 



2. Band Maxima of Chlorophyll and Bacteriochlorophyll in the Spectra of 



Living Plants 



(a) Red Band of Chlorophyll a 



Chlorophjdl is responsible for practically all absorption of green plants 

 above 550 m/i {cf. page 719), and the main red absorption peak of chloro- 

 phyll a is recognizable in all plant spectra. Hagenbach in 1870, noticed 

 that this peak is displaced by about 20 m/x toward the infrared compared 

 with its position in ether, alcohol or similar solvents; and Gerland, in 1871, 

 found that a similar shift also affects other, less prominent, chlorophyll 

 bands in the j-ellow and orange part of the spectrum. 



