996 THE LIGHT FACTOR. I. INTENSITY CHAP. 28 



the blue alga Gigarlina behaved like a typical shade plant, whereas the violet, deep-water 

 form of the .same species, I'ich in j)h3'cocyauin, maintained its jjhotosj'nthesis at full ef- 

 ficiency even in direct sunlight. 



6. Maximum Rate and Average Rate of Photosynthesis 

 under Natural Conditions 



The curve corresponding to [C'02] = 0.03% i.s theoretically not more 

 important than any other light curve of photosynthesis, but its saturation 

 value has a considerable interest because it represents the maximum rate 

 of production of organic matter hy land plants in the open air. (In dense 

 growth, or under otherwise abnormal conditions, the concentration of car- 

 bon dioxide may vary between 0.01 and 0.1%, and this must affect the 

 maximum rate of photosynthesis in some natural habitats.) 



It was stated in chapter 27 that with 0.03% carbon dioxide, and in 

 intense light, the supply of carbon dioxide has a considerable rate-limiting 

 influence, and the saturation value may therefore be below the "absolute" 

 maximum, P|||"' at the same temperature. Table 28. VI contains some 

 relevant experimental data (for a more extensive table, see Stocker 1935). 

 Most figures in this table represent the net consumption of carbon dioxide. 

 For strongly photosynthesizing plants, the corresponding values of true 

 photosynthesis are 10-15% higher; but for weakly photosynthesizing 

 plants (e. g., the arctic plants investigated by Miiller) the difference may 

 be much larger, as illustrated by the figures in parentheses. Table 28. VI 

 contains some striking contradictions, which remain to be elucidated. 

 There is a general contrast between the P""' values found by Boysen- 

 Jensen and co-workers (usually 1-10 mg. C02/hr. 100 cm.-, with the largest 

 single values not exceeding 20-25 mg.), and the much larger values reported 

 — often for the same species and under similar climatic conditions— by 

 Kostychev and other Russian plant ph3^siologists (usually 10 40 mg. 

 COo/hr. 100 cm.'-, with the largest single values reaching 80 or 100 mg.). 



Only in the case of arctic plants is there an approximate agreement between Boysen- 

 Jcnsen's co-worker Miiller, and Kostychev and his co-workers. In the case of sun- 

 adapted plants from moderate zones, the average of Danish measurements (section Ba of 

 the table) is 13 mg., that of Swedish measurements (section B6), 16 mg., and that of 

 English, Japanese and German measurements (with the exception of the early determina- 

 tions of Sachs carried out by the half-leaf starch method), 10 mg. The average of the 

 Russian analyses, listed in section Be, is as liigh as 24 mg. The results obtained by 

 Kostychev, Bazyrina and Vasiliev (1927) by the determination of the synthesized assim- 

 ilates did not differ significantly from those obtained by the same group by determina- 

 tion of absorbed carbon dioxide. 



It was mentioned on page 908 that Kostychev and co-workers attributed 

 the lower values of Boysen-Jensen to insufficiently rapid gas circulation. 



