1274 THE PIGMENT FACTOR CHAP. 32 



cultures, the r values in Table 32.1 obtained with plants belonging to five 

 different phyla all he in the range between 2000 and 5000. 



The value of l/r indicates the participation in the photosynthetic proc- 

 ess of a catalytic component, x, the total available amount of which is from 

 2000 to 5000 times smaller than that of chlorophyll: [x]o = 2 to 5 X lO"* 

 [Chl]o. We may consider [x]o = 4 X lO"" [Chljo as the "normal" value. 



This estimate may need a correction : If the catalytic component in ques- 

 tion has to operate n times in order that one molecule carbon dioxide can 

 be reduced to the carbohydrate level, the factor r must be multiplied by 

 n to obtain the number of catalyst molecules required. For example, if 

 we assume n = 8 (a plausible assumption in an "eight-quanta theory"), 

 the concentration of the yield-limiting catalyst required to explain the 

 "normal" value of t, will be [x]o = 3.2 X 10-^ [Chl]o. It is also possible 

 that the limiting catalyst has to act only on one set of intermediates {e. g., 

 on the reduction intermediates of carbon dioxide, and not on the oxidation 

 intermediates of water, or, vice versa). In this case, t will have to be multi- 

 phed by n/2 instead of by n and the "normal" value of [x]o will be 1.6 X 

 10~'[Chl]o. It is more difficult — although not impossible — to imagine 



Table 32.1 

 Maximum Oxygen Yield" in Flashing Light 



[Chi], 

 Observers Species (moles/mm.') X 10» I/7 



Emerson, Arnold Chlorella pyrenoidosa . 428 2,660 



^10-^2^ 0-606 1,980 



^^^•^^^ 0.620 2;660 



. 766 2,380 



Emerson, Arnold Chlorella pyrenoidosa {25° C.) 0.756 2,010 



(■1932^') with variable chlorophyll 1.07 2,380; 2,780 



^ ^ content 1.14 3,120 



1.49 2,310 



1.59 2,460 



Bryophyllumcalycinuin {31.5°) — 2,500; 2,600 



Chlorella vulgaris {25°) — 2,800 



Arnold, Kohn (1934) Lemna sp. (25, 26, 29°) — 2,600; 3,200; 



Nicotiana lon.gsdorffii (30, 29 °) — 2,800 ; 2,500 



Selaginella sp. (28°) — 4,200 



Stichococcus bacillaris (25, 30°) — 3,700; 5,000 

 Emerson, Green, Chlorella pyrenoidosa, different age 



Webb (1940) 2 days^ — 3,750 



4 days" — 6,180 



8 days'- - 11.120 



15 days<= — 6,650 



21 days" — 11,000 



29 days" — 14,500 



Arnold {cf. van Niel Rhodospirillurn rubrum — 400 



1941) 



<• T = oxygen yield, molecules per flash per molecule chlorophyll. 

 " Four 40 w. lamps 10 cm. from cultures during growth. 

 " One 40 w. lamp 15 cm. away. 



