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H. TAMIYA et al. 



VOL. 12 (1053) 



growth ; namely, at lower light intensities there exists a linear relationship between the 

 rate and light intensity, while at higher light intensities the rate becomes independent 

 of light intensity. 



8 10 12 14 16 18 20 22 24 



LIGHT INTENSITY IN KILOLUX 



Fig. 8. Relative rates of growth and photosynthesis as a function of light intensity at different 

 temperatures. Photosynthetic rate was measured with active dark cells and expressed in terms of g 

 organic photosynthate formed by i g dry weight of cells per day, so that it is directly comparable 

 with the growth rate defined by: Ag = ijAt X log^Q{W2lW.^), where / is the time in days, and W the 



dry weight of cells in unit volume of culture. 



2. In both photosynthesis and growth, the light-saturated rate is temperature- 

 dependent, while the light-limited rate a, i.e., the tangent of the rate-light intensity 

 curve at sufficiently low light intensity, is temperature-independent. 



3. The value of a is quite the same for photosynthesis and growth. 



4. At saturating light intensity, the growth rate is always lower than the photo- 

 synthetic rate. The temperature dependency of the former is more conspicuous than 

 that of the latter. 



It ought to be remarked that the growth rate tended to be lowered at extremely high light 

 intensities, which was especially notable at lower temperatures. Such a tendency was not observed in 

 photosynthesis, at least up to the light intensity of 50,000 lux in the experiments lasting for 3 hours. 

 At 7° C, the growth was retarded even when the light intensity was about 10,000 lux, and at 50,000 

 lux the cells completely ceased to grow within a few days, with a symptom of complete bleaching of 

 cells. The tendency of color-fading of cells was observed, though to a minor extent, also at higher 

 temperatures. In all cases, the cell suspensions grown under weaker light were dark green in color, 

 and with the increase of light intensity the color changed into light green and then into brownish 

 pale green. It is interesting to note that the occurrence of such a fading in color was dependent on 

 temperature ; for example, the light intensity under which the light green cells were formed increased 

 with temperature as follows: 2000 lux at 7°, 25,000 lux at 15' and 50,000 lu.x at 25° C. 



It was found that these color changes, except for the extreme case observed at 7"^, 

 reflect the change of relative abundance of dark and light cells in the culture. In Fig. 9 

 are shown the dark cell ratios {A) found in the steady state of growth under different 

 conditions. 



References p. 40. 



