Organ 



A distinct part of a plant or animal which carries on one 

 or more particular functions, e. g., a leaf, wing of a bird. 



Organelle 



Any part of a cell of an organism. 



Organic Matter (In Soil) 



Materials derived from plants or animals, much of it in 

 a more or less advanced stage of decomposition, cf. Humus. 



Organic Soil 



A soil composed mainly of organic matter on a volume 

 basis; containing 20 per cent or more on weight basis, e. g., 

 Muck, Peat. 



Organismic (Organismal) 



Refers to the concept that a group of organisms such as 

 a community has qualities of a higher level of organization 

 than the constituent organisms have individually; changes 

 occurring in a community are related more to the qualities 

 of the group than to those of the individual plants and 

 animals. 



Oriental Region 



One of the four continental faunal regions in the realm 

 Megagea; it includes tropical Asia and the associated con- 

 tinental islands. 



Ornithology 



The division of zoology that deals with birds. 



Ornithophilous 



Refers to flowers that are pollinated by birds such as the 

 hummingbird. 



Orogenesis 



The process of mountain formation by changes in the 

 earth's crust. 



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