THE LIGHT FACTOR IN PHOTOSYNTHESIS 



1025 



80 



E 60 



67, 90, 93, 104r, 124). Maximum absorption appears in the red and in 

 the bhie-violet regions of the spectrum and maximum transmission in the 

 green. The spectrum is composed of several bands, the maxima of 

 these as reported by Willstatter and StoU (143) for Sambucus nigra at 

 about X6750, 6240, 5850, 5430 A and loo 



o 



an end absorption from X5190 A. If 

 the percentage absorption is plotted 

 against wave-length, the bands of 

 absorption are not nearly so distinct as 

 the pubUshed spectrograms indicate, 

 owing to "contrast bands" which 

 appear in spectrograms and in visual 

 observations. An absorption curve of 

 Sambucus nigra as determined by 

 Seybold (104c) is shown in Fig. 1. 

 There is some difference of opinion 

 concerning the variability of the 

 absorption spectra of different leaves 

 (Lasareff, 62). Lubimenko (67) is of 



40 



20 



400 



c 

 o 



•"40 

 § 



to 



c 

 o 



f^20 



4- 

 C 

 01 



o 



<1> /^ 



"/OO 600 500 



Wave Lenq+hs in m(i. 



Fig. 1. — -Comparative spectral trans- 

 mission curves for: 1, dilute solution of 

 chlorophyll in acetone; 2, concentrated 

 the opinion that each leaf possesses its solution of chlorophyll in acetone; 3, 



own transmission spectrum. ^«^^' ^'^^^^''^^ ^^>«- (Sei/feoZd, I04c.) 



That variations in transmission spectra of leaves should exist seems 

 inevitable. The transmission curves are dependent upon the physical 

 structure of the leaves as well as upon their pigment content. Both 

 of these properties differ to some degree in each individual leaf. 



Of primary importance is exact 

 information regarding the proportion 

 of light which is absorbed by the 

 pigments of the leaf, especially those 

 of the chloroplasts. A favorite method 

 of arriving at this value has been 



7,000 6,000 \ 5,000 



Wave Lengths in A 



Fig. 2. — Transmission spectra 

 leaves, Acer negundo: TF, white leaf; of an albinO leaf of the Same SpecicS. 



G. green leaf. (.s.y6oW. 104c.) j^ ^^^ however, not justifiable to 



assume that the amount of light which is absorbed by an unpig- 

 mented leaf is equal to the amount of light which is absorbed by 

 the colorless portion of a similar leaf (Willstatter and Stoll, 143, page 120) 

 (Seybold, 104a, 6). The amount of light absorbed by the colorless 

 substance in the pigmented leaf is, on a percentage basis, less than in the 

 unpigmented leaf, because each volume unit within the green leaf receives 

 less light energy than the corresponding volume unit of the white leaf. 

 Also the reflection from the surface of an unpigmented leaf is much higher 

 than from a pigmented one. In Table 2, are given the mean values 



4,000 through the comparison of the absorp- 

 , tion of the pigmented leaf with that 



of '■ " 



