r 54 Ingvar Jorgensen and Walter Stiles. 
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 n 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 2T. However, an examination of Miss Matthaei’s figures are 
sufficient to show that the choice of2T as the temperature coefficient 
between 5 n C and 25°C was fully justified. Below 5°C the temperature 
