INFLUENCE OF TEMPERATURE 29 



Qi = r6. Comparable observations have been made by 

 Yabusoe * and also by Lundegardh f who found the tempera- 

 ture coefficient to be 1 -03-1-45 at 30°-35° in a strong light 

 and with an atmosphere enriched to 1-2 per cent, of carbon 

 dioxide. The maximum rate occurred at 35 C. and provided 

 that the initial heating was not too prolonged, the time factor 

 was ill-defined. Blackman observed that under strong illu- 

 mination or in a high concentration of carbon dioxide, a rise 

 of 10° in temperature, from 15 to 25 , roughly doubles the 

 velocity of photosynthesis ; this is termed by Warburg J the 

 " Blackman Reaction " and it indicates that in the condi- 

 tions specified, the rate of carbon assimilation is determined 

 by a chemical rather than a photochemical reaction, for, as 

 has been seen, with a low light intensity a rise in temperature 

 does not affect the rate of the reaction. The Blackman 

 reaction was originally thought by Warburg to be a prelimi- 

 nary reaction which led to the formation of an unstable deri- 

 vative of carbon dioxide which was decomposed by light, but 

 later he and Uyesugi adopted Willstatter's idea that in an 

 early phase of photosynthesis a peroxide is formed and that 

 the Blackman reaction consists in the separation of oxygen 

 from this peroxide. 



CH 2 0[0 2 ] -> CH 2 + 2 . 



In much experimental work on photosynthesis, moderate 

 and higher temperatures have, for obvious reasons, been em- 

 ployed ; it is, however, to be remembered that carbon as- 

 similation takes place at extreme temperatures according to 

 the specific physiology of the plant. McGee § found that 

 Opuntia can function at 55 C. and Matthaei || found a measur- 

 able photosynthesis in the cherry laurel leaf at — 6° C. 

 Henrici *\ similarly observed a definite photosynthesis in lichens 

 at — 20° C. and in alpine phanerogams at — 16 C. 



* Yabusoe: id., 1924, 152, 498. f Lundegardh: id., 1924, 154, 195. 



% Warburg : " Biochem. Zeit.," 1919, 100, 230; 1926, 166, 386. 

 Warburg and Uyesugi : id., 1924, 146, 486. 



§ McGee : " Year-Book Carnegie Inst. Wash.," 1921, 20, 47. 



|| Matthaei : loc. cit. 



If Henrici : " Verhand. nat. Ges. Basel," 1919. 3<>, 43 : 1921, 3 2 > io 7- 

 See also Ewart : " Journ. Linn. Soc, Bot.," 1896, 31, 364. Wurmser and 

 Jacquot : " Bull. Soc. chim. biol.," 1923, 5, 305. 



