SOIL CONDITIONS AFFECTING PLANT GROWTH 37 



the protoplasm should remain healthy and vigorous. Now 

 the temperature range over which protoplasm lives and the 

 somewhat delicate adjustment of the processes holds together 

 is very restricted ; beyond a certain point, which varies with 

 different plants, further temperature increases do not cause 

 more growth, but throw the adjustment out of gear. Thus 

 the curve begins to bend over. 



The student will observe a close similarity between this 



Qu 



A 



TEMPERATURE 



FIG. 4. Influence of temperature on enzyme action, showing fall in quantity 

 but increase in activity as temperature rises. (Duclaux.) 



curve and that obtained by Duclaux 1 for the relation between 

 enzyme action and temperature. In Fig. 4 AB shows the 

 relation between enzyme action and temperature so long as 

 the activity remains unimpaired ; CD shows the relation 

 between temperature and quantity of enzyme, the enzyme 

 being destroyed as the temperature rises ; AOE is the resul- 

 tant curve showing the relation between temperature and the 

 activity of a given initial quantity of enzyme. 



1 E. Duclaux, T-raite de Micro biologie, Tome 2, Paris, 1899. 



