COMPENSATION POINT 



981 



suppl}' of carbon dioxide) the linear range usually extends up to 5 or 10 

 kerg/cm.2 sec, corresponding to 1-2 klux of white light. In some cases, 

 however, the first signs of curvature have been observed — despite ample 

 supply of carbon dioxide — as earl}'- as at 1 kerg/cm.- sec, or 200 lux; while 

 in others, the linear increase continued up to 50 or even 100 kerg/cm.'^ sec, 

 i. €., 10-20 klux (c/. figs. 28.1 and 28.14B). 



Theoretically, no exact definition of the linear range can be given, since 

 all light curves probably are hyperbolae (or curves of a higher order) and 

 can only approach straight lines asymptotically. A formal definition of 

 the upper limit of the linear range could thus be given only in terms of a 

 definite deviation from linearity. 



200- 



5 10 15 20 



LIGHT INTENSITY, einstein/cm.^ mm 



Hg. 28.14A. Approximate linearity of 

 light curves of Chlorella in white light up 

 to ca. 1300 lux (or G.5 kerg/cm.- sec.) 

 (after Emerson and Lewis 1941). 



E 



6 



o 



I- 

 < 



C/5 



< 



_J 

 < 



I- 



< 



2 4 6 8 



LIGHT INTENSITY 



Fig. 28. 14B. Light curves in purple 

 hactciia in soilium light (after Eymers 

 and Wassink 1938) (showing linearity up 

 to GO kerg/(cm.2 sec.)). Light hitensity 

 in (erg/cm.^ sec.) X 10^ 



Wassink (1946) gave incident intensities of monochromatic yellow light 

 at which the yield of photosynthesis of nine horticultural plants showed 

 16% deviation from proportionality {cf. Table 28.11). 



Kok (1948,1949) and van der Veen (1949) found that the linear range 

 may consist of two segments, the lower one up to twice as steep as the up- 

 per one {cf. chapter 29, p. 1113). 



3. Compensation Point 



The compensation point is the light intensity Ic at which photosynthesis 

 is balanced by respiiation. so that the net gas exchange is zero. 



