MATERIAL 



835 



})hyll) increased rapidly at first — in agreement with Noddack and Eich- 

 hoff's observations — and then approached constancy {cf. chapter 31 for 

 more detailed discussion of the relation of the rate of photosynthesis to 

 chlorophyll content). 



Suspensions like those in Table 25.1, placed in vessels 1-3 cm. deep, 

 absorb 20-50% of incident white light. If complete absorption of visible 

 light is desired (as in Warburg and Negelein's procedure), suspensions 

 containing more than lO'^ cells per milliliter must be used in vessels of the 

 same depth. 



The photosynthetic efficiency of Chlorclla suspensions has been related 

 to many factors, such as the intensity of light (Warburg) and the rate of 



1.3 

 1.2 



5 1.0 



a> 



(n 0.9 

 ^ 0.8 

 0.7 

 0.6 

 0.5 

 0.4 



6 8 10 12 14 16 18 20 22 24 

 TIME IN BUFFERS, hr. 



Fig. 25.1. Relative rate of photosynthesi.s in Chlorella vulgaris as a 

 function of the lengthof e.xposure of the cells to 0.1 M solutions of KHCOg, 

 NaHCOs, or varying mixtures of the two bicarbonates (after Pratt 1943). 



gas supply during growth (Burk), or the "oligodynamic" effects of small 

 quantities of rare elements icf. Emerson and Lewis 1939). However, 

 some investigations on the quantum yield of photosynthesis (cj. chapter 

 29) indicate that these conditions may influence mainly the gas exchange 

 in the first few minutes of exposure to light, and have little effect on the 

 steady rate of photosynthesis (cf. Table 25.1). 



According to Emerson and Green (1938) the photosynthesis in Chlorella 

 is insensitive to Avide variations in pH (Vol. I, p. 339) ; consequently, 

 these algae can be used in acid as well as in alkaline solutions (Con- 

 cerning the difference between quantum yields of Chlorella in aci'd and 

 alkaline buffers, see pp. 1096, 1107.) Pratt (1943^) observed that the rate 

 of photosynthesis of Chlorella in strong light declined to 40% of its initial 

 value after nine hours in a 0.1 M NaHCOs solution and then remained 



