Evapotranspirometer 



A soil-filled container covered with living vegetation and 

 supplied with water to measure transpiration and evapora- 

 tion. 



Even-aged 



Refers to a stand of trees in which only small differences 

 in age occur between the individuals; in young stands dif- 

 ferences should not exceed 10 to 20 years, in mature stands 

 not more than 30 to 40 years, cf. Age-class. 



Evolution 



The process of Natural or Artificial selection acting upon 

 genetic diversity in organisms. 



Evolution, Convergent 



The development during the course of evolution of simi- 

 lar structures or habits in organisms that are not closely re- 

 lated taxonomically. cf. Taxonomy. 



Exchange Capacity 



See Cation-exchange capacity. 



Exclosure 



An area fenced to exclude certain kinds of organisms, cf. 

 Enclosure. 



Exclusive Species 



A species belonging to the highest Fidelity class (Braun- 

 Blanquetj, one which occurs exclusively or almost so in "a 

 specific kind of vegetation unit. 



Exclusiveness 



The degree in which a particular species is restricted to 

 a particular kind of community to the exclusion of other 

 communities, cf. Exclusive species, Fidelity. 



Excretion 



The elimination of substances from the bodies of or- 

 ganisms. 



135 



