706 LIGHT ABSORPTION BY PIGMENTS IN VIVO CHAP. 22 



maxima (at 422 and 467 m^t) and one chlorophyll maximum (at 500 m^) 

 are lost by the superposition of the absorption curves. 



Upon closer examination, carotenoid maxima can be identified at least 

 in some plant spectra. Peaks, which probably belong to the carotenoids, 

 are noticeable, for example, at 468 and 486 niju in the spectrum of the leaves 

 of Fatsia (Fig. 22.13, cf. also Table 22.III), and at 473 and 488 m/x in that 

 of Chlorella (Fig. 22.22). If one attributes both these peaks to luteol, 

 whose absorption bands in ethereal solution are situated at 442 and 472 

 m/i (cf. Table 21.1), it follows that the carotenoid bands in live cells are 

 shifted toward the red by as much as 25-30 m/x. (Av = 1250 cm.-^ or 

 three times the shift of the red and blue-violet absorption bands of chloro- 

 phyll.) Emerson and Lewis (1942) postulated, in their interpretation of 

 the Chroococcus spectrum (cf. page 723), a shift of the carotenoid bands 

 in vivo by 14 m/x from their position in ethanolic solution; according to 

 Table 21.1, this corresponds to a shift by 24 m/x relative to ethereal solu- 

 tion, in good agreement with the preceding estimate (25-30 niju) . 



Menke (1940) extracted chlorophyll from chloroplast preparations 

 (made from spinach leaves; cf. Vol. I, page 369) ; and found that a brick- 

 red residue was left. A suspension of this residue in water showed absorp- 

 tion bands at 490 and 540 m/x — much further toward the red than the caro- 

 tenoid bands have been observed in live green plants (470 and 490 m/x 

 were the positions quoted above for Fatsia leaves and Chlorella cells). 

 Moistening with ether led to a change of color, and a shift of the absorption 

 bands to their usual positions in carotenoid solutions (442 and 472 m/x) . 



The absorption spectrum of the brown alga Laminaria was found by 

 Menke to exhibit bands— probably due to fucoxanthol— at even longer 

 waves, namely, 499 and 545 m/x- Heating to 70° C. led to a shift of these 

 bands to below 510 m/x, and to a color change from brown to green. 



The transmission curves of diatoms (Nitzschia dissipata) published by 

 Wassink and Kersten (1946), as well as the absorption curves of brown algae 

 given by Seybold (1934, 1943), clearly show an increased absorption (in 

 comparison to the green algae, such as Ulva or Chlorella) in the region 500- 

 580 m/x, but give no indication as to the position of the absorption peak 

 (or peaks) of the carotenoid responsible for this absorption. From the 

 comparison of the transmission curves of live diatoms (and of aqueous col- 

 loidal cell extracts, whose brownish color is similar to that of cell suspen- 

 sions) with the transmission curves of the (green) pigment exti-act in an or- 

 ganic solvent (methanol and petroleum ether), Wassink and Kersten esti- 

 mated that the fucoxanthol bands are shifted in vivo by about 20 m/x 

 (corresponding to about 700 cm.^^), toward the longer waves; but this esti- 

 mate is not at all reliable because of the absence of pronounced maxima. 

 These curves, and Karrer's absorption curves of fucoxanthol in solution, 

 make it appear uncertain whether the increased absorption of diatoms and 

 brown algae in the green (500-560 m/x) is due mainly (or exclusively) to a 



