Temperature. 79 



experiment. Obviously it would also depend on the previous history 

 of the leaf as regards temperature. 



In regard to the existence of the time factor Blackman points 

 out that the rate of hydrolytic action of enzymes always shows a 

 marked optimum temperature effect, and he cites Kjeldahl (1879) 

 who showed that malt diastase hydrolysed increasing quantities of 

 starch up to about 63"C after which the action fell off quickly, 

 becoming nothing at 86''C, this being due to the destruction of the 

 enzyme by heat. The apparent production of an optimum is thus 

 due to two opposed processes, the hydrolytic action of the enzyme 

 and the destruction of the enzyme by heat. 



This characteristic of enzyme actions was later elaborated by 

 Tammann (1892, 1895) and by Duclaux (1899) and it has come to 

 be called Tammann's principle. Fig. 12, taken from Duclaux, 

 illustrates clearly how the optimum is produced. The curve AB shows 

 the relation between temperature and the enzyme action if the 

 enzyme activity remains unimpaired, the curve CD represents the 

 relation between temperature and quantity of enzyme, and the 

 curve AOE represents the actual curve between temperature and 

 the enzyme action. 



Recently some Continental writers (Kanitz 1915, Rahn 1916) 

 have taken the trouble to point out the application of Tammann's 

 principle to Blackman and Matthaei's results. Not only did 

 Blackman himself point out the similarity of his results with those 

 in the case of enzyme actions, but he also recognised that the 

 matter was probably more complex. Thus he says " Physico- 

 chemical finality is not to be attained in this matter, but special 

 research might at least show how far the recorded optima for 

 assimilation and respiration are real metabolic truths and how far 

 they are illusions of experimentation." 



With the further criticism of Rahn we need not deal, as it 

 attempts to explain why Blackman did not get a result which as a 

 matter of fact he actually obtained. 



Kanitz also criticises Blackman on account of the manner in 

 which the curve of initial assimilation values at high temperatures 

 is obtained. He points out that the number taken by Blackman 

 for the temperature coefficient of assimilation in the case of Cherry 

 Laurel was quite arbitrary ; that it might have been 2-4 equally 

 with 2-1. However, an examination of Miss Matthaei's figures are 

 sufficient to show that the choice of 2-1 as the temperature coefficient 

 between 5''C and 25°C was fully justified. Below 5°C the temperature 



