INFLUENCE OF TEMPERATURE 27 



essential that the previous history of all the material employed 

 should be the same. 



In Primus laurocerasus Matthaei found that for each tem- 

 perature to which the leaves were subjected there is a definite 

 amount of carbon assimilation, the maximal assimilation for 

 that temperature, which cannot be exceeded and cannot be 

 attained unless the illumination be of sufficient intensity and 

 the carbon dioxide be adequate in amount. These maximal 

 amounts of assimilation increase rapidly with rising tempera- 

 tures, but at the higher temperatures the initial rate for 

 that temperature cannot be maintained for long but falls off 

 regularly at a rate dependent on the temperature ; the higher 

 the temperature the quicker the fall, but the rate of fall is 

 not maintained. Thus there is a time factor for the higher 

 temperatures. Fig. 5 summarizes the results obtained by 

 Matthaei ; it will be seen that the turning-point is 37-5° C. 

 which was found to be within a few degrees of the tempera- 

 ture fatal to the leaf. 



The results obtained for temperatures below 25 C. con- 

 formed to van't Hoff's Law, the coefficient of increase in the 

 rate of carbon assimilation for a rise of io° C. being 2-1. In 

 subsequent investigations Blackman and Matthaei found the 

 assimilation coefficient for the leaves of Helianthus tuberosus 

 to be K 10 = 2-3, whilst for Elodea, K 10 = 2-05.* The culmi- 

 nating point of the assimilatory curve (Fig. 5) in respect to 

 increasing temperature is important and is paralleled in en- 

 zyme action ; in view of the results obtained by Willstatter 

 and Stoll, it is not unlikely that the inhibition or destruction 

 of an enzyme at these higher temperatures may be the limiting 

 factor. Osterhout and Haas f obtained a coefficient of i-8i 

 for Ulva rigida between if and 27 C, a figure which, accord- 

 ing to Smith $ is probably too low. Warburg § investigated 

 the same phenomenon in Chlorella and thus avoided the diffi- 

 culties inseparable from morphological complexity with a 

 varying internal temperature and possibly an uneven rate of 



* Blackman and Smith : " Proc. Roy. Soc," B, 1911, 83, 389. 



f Osterhout and A. R. C. Haas : " Jour. Gen. Physiol.," 1919. '» 2 95- 



\ Smith : " Ann. Bot.," 1919, 33» 5*7- 



§ Warburg : " Biochem. Zeit.," 1919, 100, 230. 



