700 LIGHT ABSORPTION BY PIGMENTS IN VIVO CHAP. 22 



22.23 for Chroococcus, and 22.24 for Oscillatoria). The "red shift" is recog- 

 nizable in all of them, particularly in the last three figures, in which the 

 spectra of extracted pigments are compared with those of live cells. True. 

 Noddack's figure (fig. 22.21) indicates only a comparatively small shift 

 —from 660 to 668 mju— in live Chlorella cells, but Katz and Wassink (1939) 

 and Seybold and Weissweiler (1942) found, for the wave length of the red 

 band in Chlorella, the value generally given for leaves — about 680 111^. 

 Finally, it was stated on page 653 {cf. figs. 22.15, 22.16 and 21.29) that the 

 red absorption peak is situated at about 675 m/z also in aqueous chloro- 

 plastin extracts. The position of the red absorption peak in live cells is 

 thus determined, beyond doubt, by the state of the pigment (which is pre- 

 served, to a certain extent, in colloidal extracts), and not by geometrical- 

 optical conditions. 



It has often been suggested that the position of the red absorption 

 maximum of chlorophyll (and the number and position of secondary 

 maxima) varies in different species. Table 22. Ill gives a summary of ex- 

 perimental results. It shows the red peak at 675 mn ± 15 mn, with the 

 average position corresponding to a "red shift" of 15 m^u, or 370 cm.-^ 

 (compared to the position of the corresponding absorption band in ethereal 

 solution of chlorophyll a). The extreme limits of variation of X^ax. in 

 Table 22. Ill are 665 and 690 m^ — quite a wide range. However, because 

 of the diffuse character of the spectra, the position of the maximum often 

 cannot be determined precisely. It is therefore not certain whether any 

 of the tabulated variations in X,„«j are real. (It will be noticed that four 

 values are given for Chlorella, 680, 668, 672 and again 680 m/z!) 



Lubimenko (1927), who made photographs of the absorption spectra of 

 a large number of leaves, insisted that they do exhibit real differences — not 

 only in the positions of the main peak, but also in the number end positions 

 in the secondary absorption maxima in the yellow, green and blue. 



According to Lubimenko, the spectra of some species ("group 1") contain eight 

 bands in the visible region. An example is nettle {Urtica dioica), with the following 

 bands: I, 680-660; II, 650-645; III, 630-606; IV, 600-570; V, 550-540; VI, 

 512-480; VII, 450-430; and VIII, below 420 m^- The bands III, IV and V become 

 visible only when two leaves are used. Leaves of "group 2," which includes the largest 

 number of species, show seven bands (band VII of the above list is missing). Elodea 

 canadensis and Hedera helix belong to this group. "Group 3" (e. g., Prunus laurocerasus) 

 shows only six bands (bands I and II are fused). Finally, plants of "group 4" {e. g., 

 the alga Ulva lactuca) have onW four bands: I, II, V, VI and VIII. The absence of 

 band III in these spectra is particularly remarkable. Table 22. IV shows the limits of 

 variation in the positions of the above-listed bands, as given by Lubimenko, and also 

 gives a tentative identification of these bands with the bands of chlorophylls a and b in 

 solution. According to Lubimenko, in passing from species to species, different bands 

 are displaced by different amounts, or even in different directions. 



