FACTORS OF ENVIRONMENT. 469 



reproduction, the temperature which is most favorable varies in 

 the different processes. For each process there is a minimum, 

 optimum, and maximum temperature, the minimum and maxi- 

 mum representing the lowest and highest temperatures at which 

 the process can take place, while the optimum is the temperature 

 most favorable for the process. The absolute optimum, which 

 corresponds to the highest intensity of a function, therefore is 

 not always the most favorable temperature for the plant as a 

 whole. For in the case of transpiration and respiration at the 

 absolute optimum temperature these processes would take place 

 so rapidly that the plant would be injured. On the other hand, 

 the harmonic optimum corresponds to the most favorable inten- 

 sity of a function. So the "ecological optimum is composed of 

 the harmonic optima." The cardinal temperature points are 

 the most favorable temperatures for the various processes. 

 From germination of the seed through growth and reproduction 

 there is a general rise of the curve which represents the cardinal 

 points for the various processes, but there is a more or less regu- 

 lar fluctuation or alternation of the successive cardinal points; 

 especially is this the case with many plants in temperate and 

 arctic regions. For example, the cardinal point for the growth 

 function is often higher than the cardinal point for flower forma- 

 tion and reproduction. 



911. Acclimatization. When plants are changed from warm 

 zones to colder ones, or from cold zones to warmer ones, either 

 by man or by the laws of migration, if they are able to reproduce 

 and propagate themselves in the new region it is because they 

 have become adapted to the changed conditions of temperature. 

 Tliis adaptation of an organism to changed climatic conditions 

 is called acclimatization. Acclimatization to changed temperature 

 conditions is possible in the case of those plants which are able 

 to adjust the cardinal points for the different life processes to 

 the new temperatures. This is accomplished by raising or 

 lowering the cardinal points for the different functions. It is a 

 well-known fact that some plants taken from cool zones to warmer 

 ones are able to raise the cardinal points for processes of nutri- 



