GROWTH 



219 



the growth rates decrease from day to day. With Phomopsis citri, 

 the maximum growth rate, i.e. the optimal temperature is constant 

 at 27.5°C. Above 31°C. the growth rate decreases from day to day. 

 With Diplodia natalensis, the optimum temperature shifts from 

 30°C. to 25°C. and at 30°C. and above, the growth rate decreases 

 with time. 



Considering, then, the Tammann principle established, 

 we have a good explanation why the upper range of 

 temperature for growth is limited, why there is a maxi- 

 mum and an optimum temperature which are unknown 

 with common chemical reactions. 



For the range of normal growth temperatures, the 

 most accurate and extensive data of the older research 

 are those of Ward, Max Miiller, and Barber. All three 

 differ in their technique. Ward measured the increase 

 in the length of the cells of B. ramosus under the micro- 

 scope; Miiller counted his bacteria by the plating method; 

 Barber grew one single cell of Bad. coli in a hanging 

 drop and counted the number of cells under the micro- 

 scope after a given time. 



Table 56. — Growth op B. ramosus at Different Temperatures 



