352 RADIATION BIOLOGY 



chlorophyll, does not reflect infrared to such a high degree as leaves do. 

 Most leaves absorb far more light than this very pale lettuce leaf does. 

 The bean leaf shown in Fig. 6-26 is much more typical of ordinary foliage. 

 It will be noted that the reflection is quite low, amounting to less than 

 20 per cent even in the region around 550 m^u, where the absorption is 

 the smallest. Five to ten per cent is more or less normal in red and blue, 

 and the reflection rarely reaches a value so high as 20 per cent even in 

 the green. In this particular leaf it happens that reflection and trans- 

 mission are very nearly equal. In Fig. Q-2d we have a comparison in 

 absorption among three leaves of Corylus avellana. The lower curve is 

 for a leaf containing smaller amounts of pigment than the middle leaf. 

 The top curve, similar otherwise to the middle leaf, contains a large 

 amount of anthocyanin, a photosynthetically inactive red pigment. 



In Fig. 6-3a is given the optical-density curve of the green alga Chlamy- 

 domonas, which is compared with the brown alga Laminaria. Both these 

 curves have been adjusted to a density of 0.6 at the height of the red 

 peak. The lack of chlorophyll b in Laminaria is clearly shown by the 

 steepness of the red peak on the short-wave side and also by the shift 

 in its position as compared with that in leaves and in Chlamydomonas. 

 Furthermore the difference between the absorption of fucoxanthin in 

 Laminaria and that of the carotenoids of Chlamydomonas is evident from 

 the shoulder in the absorption curve of Laminaria at a wave length of 

 about 510 m/x, whereas the principal carotenoid maximum in Chlamy- 

 domonas comes at about 480 m^u. A similar comparison may be made 

 between the Laminaria curve and that for a leaf of Aponogeton in Fig. 

 6-36. Also, in Fig. 6-36 is an absorption curve for an extract (presum- 

 ably in methanol) of the same leaf which was prepared so as to contain 

 the pigments in an area of solution equal to that of the leaf. These 

 curves are therefore directly comparable. The same factor that was 

 used in adjusting the leaf curve to a density of 0.6 was applied to the 

 extract curve. Other comparisons by Seybold and Weissweiler (1942a,b) 

 generally show a greater absorption in the live material than in the 

 extract, even at the peaks. This set of data in which the peaks are 

 nearly equal in height was selected so that the shapes of the two curves 

 might be directly compared. It is obvious that a quantitative match 

 of the leaf spectrum cannot be made by any simple modifications such 

 as wave-length shifts and broadening of the absorption spectrum of the 

 extract. A close approximation to the true optical-density curve of the 

 pigment complex of leaves is, however, probably given by the curve in 

 Fig. 6-3c. This represents the optical density of a water extract of 

 ground spinach clarified by digitalin. This curve comes much closer to 

 matching the absorption spectrum of living material than does that of 

 the organic solvent extracts. This material contains both chlorophylls 

 and carotenoids, presumably in combination with proteins. A chloro- 



