834 METHODS OF KINETIC MEASUREMENTS CHAP. 25 



Table 25.1 



Characteristics of Two Chlorella pyrenoidosa Suspensions 



(after Noddack and Eichhoff 1939) 



" Maximum photosynthesis, as obtained with an illumination of 30,000 lux (white 

 light), in a carbonate-bicarbonate buffer solution. 

 ^ "Assimilation number." 



plast, which ahnost encloses the central part of the cell with the nucleus. 

 Their chlorophyll content is remarkably high — from 2.5 to 5% of the dry 

 weight, the higher concentrations occurring in cells grown in weak light. 

 Table 25.1 shows, as an example, the characteristics of tw^o Chlorella pyre- 

 noidosa suspensions used by Noddack and Eichhoff — one grown in weak 

 light and the other in strong light. According to the table, the "shade 

 cells" are two times larger than the "light cells," and contain almost twice 

 as much chlorophyll (in per cent of dry weight) , which means three to four 

 times more chlorophyll molecules per cell. Despite their lower chlorophyll 

 content, the light cells can produce as much oxygen per milliliter of cell ma- 

 terial as the shade cells, so that their oxygen production per unit weight of 

 chlorophyll (the "assimilation number," cf. chapter 28) is about twice as 

 large as that of shade cells. 



Sargent (1940) gave 3.3% and 6.6% of dry weight as the chlorophyll 

 contents of light cells and shade cells of Chlorella, respectively. Myers' 

 results (1946') agree with those of Noddack and EichhofT and of Sargent in 

 showing a higher concentration of chlorophyll in cells grown in weak light, 

 but deviate from those of Noddack and EichofT in so far as amount of the 

 green pigment in a single cell is concerned. In Myers' cultures, the aver- 

 age volume of cells increased rather than decreased with increasing light in- 

 tensity of cultivation (from 28 X 10^ cells per milliliter at 6 foot candles to 

 6 X 10^ cells per millihter at 360 foot candles). The growth in cell volume 

 almost exactly balanced the decrease in cellular pigment concentration, so 

 that the total number of chlorophyll molecules per cell remained practically 

 constant, independently of the intensity of illumination. 



The maximum capacity for photosynthesis of Myers' cultures (related 

 to one milliliter of cell material) showed a sharp increase with increasing 

 intensity of illumination during cultivation, between 5 and 25 foot candles, 

 remained constant between 25 and 60 foot candles and then declined. 

 Since at the same time the concentration of chlorophyll declined steadily, 

 the "assimilation number" (maximum photosynthesis per gram chloro- 



