1170 THE LIGHT FACTOR. III. COLOR CHAP. 30 



Table 30.V 

 Quantum Yields of Diatoms (after Dutton and Manning, 1941) 



7/7 (red) 



0.77 1.20 1.04 ±0.05 



0.96 1.27 1.10 ±0.04 



X, m^ tenoids," From To Av. From To Av. 



^2^L+fJl^^^"^f^ ^n ^Rlf ^-^I^ H-^S 0.90 1.43 1.08 ±0.08 

 660.0 (red band axis) 



435.8 (blue) 



665 . (red band axis) 



496.0 (blue-green) 93 0.039 0.081 0.059 ^ ^^ 0.80 0.75 ± 0.03 



660.0 (red band axis) 



546 . 1 (green) 

 665 . (red band axis) 



" Calculated by shifting all curves in figure 22.46 toward the red by 20 m/j. (for a 

 criticism of this procedure, see page 726). Chlorophyll c absorption neglected! 



and concluded that the quantum yields in the violet, blue and green are 

 practically equal to that in the red, despite the fact that in the first two re- 

 gions 40-50% of the light must be absorbed by the carotenoids, whereas 

 in the last one all absorption is due to chlorophjdl. Dutton and Manning 

 therefore suggested that all carotenoids present in diatoms must act as 

 sensitizers of photosynthesis. The value of 7 in the blue-green, at 496 m/x, 

 was definitely lower. Dutton and Manning suggested that this may indi- 

 cate a lesser efficiency of carotene and luteol as compared with fucoxanthol. 

 According to their calculations, the relative contribution of fucoxanthol to 

 the total absorption by carotenoids was less at 496 nifx than at the shorter 

 wave lengths. 



This assumption is derived from observations in the extract, in which fucoxanthol 

 shows an absorption spectrum terminating sharply at 500 m^ (fig. 2 1.35 A), and a maxi- 

 mum practically coincident with that of luteol. However, this apparently does not apply 

 to fucoxanthol m vivo (p. 706); and some recent observations on e.xtracts also showed 

 absorption extending to 550 m^ (cf. fig. 21.36). 



The brown color of the algae indicates a considerable spread of the blue-violet ab- 

 sorption region toward the longer waves; and it is plausible — although it cannot be 

 proved — that the pigment responsible for this spread is fucoxanthol. (A possible alter- 

 native is to ascribe part of it to chlorophyll c, although its band lies, in e.xtracts, on the 

 short-wave side of that of chlorophyll a.) 



As an alternative, Dutton and Manning suggested that an unkno\vn 

 pigment, with absorption restricted to a narrow region around 500 m/x, 

 may be responsible for the minimum in the yield curve at 496 m/x. This 

 result may also be related to Emerson and Lewis' observations of a selec- 

 tive stimulation of respiration in Chlorella by light in the region of 480 mju. 



Dutton and Manning pointed out that the participation of the carot- 

 enoids in photosynthesis of Nitzschia closierium is indicated, not only by 



