246 



ENVIRONMENTAL CONDITIONS. 



shown on plate 34, may be distinguished. These temperature prov- 

 inces are shown on figure 1, reproduced from plate 40, for ready- 

 reference here. 



Table 10. 



Of course, it is not expected that any two charts, based upon different 

 forms of climatic indices, will agree as to details. Thus, the Pacific 

 coastal region is seen to be mostly included in the cool province on 

 plate 40, or figure 1, while it lies mostly within the medium province on 

 plate 34. What particular form of temperature index, or what com- 

 bination of such indices, will be found most valuable in distinguishing 

 the climatic zones for studies of dynamic plant geography remains to 

 be determined, but it may be safely predicted that no single form of 

 index will be sufficient for the purpose of ecological and agricultural 

 climatology. It is unfortunate that Merriam's zones (our plate 37) 

 and the unsatisfactory terminology that goes with them should have 

 been allowed to become stereotyped; climatic temperature conditions 

 have many dimensions and the useful comparison of climates requires 

 the employment of many more than a single one of these. 



III. MOISTURE CONDITIONS. 

 1. INTRODUCTORY. 



As has been emphasized earlier in the present part (page 120), the 

 moisture condition immediately effective to control plant activity is 

 the water-content of the particular cells and tissues involved, and if it 

 were possible to study the duration and intensity aspects of this condi- 

 tion such a study ought to be fundamental for the ecological relations 

 with which we have to deal. As in the case of the temperature relation, 

 however, it is impossible to make any progress at present by attacking 

 the problem in this ideally logical manner ; here also it is necessary to 

 consider less immediate conditions and to pass to what is considered 

 as the external environment, without even attempting at present to 

 inquire, in more than a very superficial way, concerning the nature of 

 the internal water-relations which directly determine plant phenomena. 

 Our analysis of the matter before us proceeds somewhat as follows : 



