ACTION SPECTRUM OF BROWN ALGAE IIG'J 



comparatively high intensit3^ Dutton and Manning (1941) arrived at a 

 similar conclusion by a procedure which was much more satisfactory — at 

 least, in principle — namely, the determination of quantum j-ields in weak 

 and trul}^ monochromatic light. Because the method of Dutton and Man- 

 ning is so much more adequate than that of Montfort (c/. the criticism of 

 Emerson 1937) we will discuss their experiments first. 



Dutton and Manning used the dropping mercury electrode for the 

 determination of oxygen (c/. chapter 25, page 850). The diatom {Nitzschia 

 closierium) was found to be more sensitive than Chlorella to merciuy; how- 

 ever, its resistance was sufficient to permit measurements of 30 minutes 

 duration without marked poisoning. 



Chromatographic analysis of the pigments of Nitzschia closierium re- 

 vealed the presence of chlorophyll a, carotene, luteol, fucoxanthol and prob- 

 ably flavoxanthol, but showed no trace of chlorophyll h. No mention was 

 made of chlorophyll c, which was subsequently found by Strain and Man- 

 ning (Vol. I, p. 406) in diatoms and other broMTi algae. Analysis of the 

 absorption spectmm of the extract (c/. fig. 22.46) indicated that in methanol 

 solution at least one half the absorption between 400 and 550 m/i was due 

 to the carotenoids. This is a much larger proportion than in green plants 

 (c/. page 1150); it indicates that the ratio chloroph.yll a/total carotenoids 

 was, in the investigated diatoms, considerably lower than 3/1 (which is 

 the average for brown algae listed in Table 15.III). 



Monochromatic light from a high-pressure a. c. mercury arc was used 

 for illumination (the effect of intermittency being considered unimpor- 

 tant), as well as bands isolated from the light of an incandescent lamp by 

 appropriate filters. The density of the suspensions was such as to give 

 about 50% absorption in the red, and 75% in the blue. Two portions of 

 the same suspension were placed in two vessels, and a simultaneous deter- 

 mination of the quantum yield was made in both of them, the one vessel 

 being illuminated with violet, blue or green light, and the other with red 

 light. Table 30. V shows the results. This table indicates that the 

 individual y values varied, for each wave length, within wide limits {e.g., 

 in the red, from 0.038 to 0.100); possibly because of various degrees of 

 mercury poisoning, or other factors affecting the vitality of the cells. The 

 conclusions therefore depended entirely on the ratios of the yields obtained 

 in light of different color, in simultaneous experiments with two aliquots of 

 t he same cells. Table 30.V shows that even these ratios varied widely (e. g., 

 from 0.90 to 1.43 in the comparison of yields in violet and red light). The 

 most consistent was the series of measurements at 496 m^u, where seven 

 determinations all gave, for the ratio (quantum yield in blue-green)/ (quan- 

 tum yield in red) values between 0.07 and 0.08. By averaging the ratios, 

 1 )utton and Manning arrived at the values in the last column of Table 30.V. 



