Orographic 



Refers to mountains, or to relief characteristics of the 



land. 



Ortet 



The plant from which members of a Clone (q. v.) were 



derived, cf. Ramet. 



Orthogenesis 



The trend in the evolution of organisms in a particular 

 direction for a long time. cf. Genetic drift, Sewall Wright 

 effect. 



Orthokinesis 



The random movements of an organism that decrease 

 in rate from one part of an environmental gradient to an- 

 other part, e. g., a meal worm moving from the moist part 

 of a gradient and congregating in the drier part. cf. Klino- 

 kinesis, Klinotaxis, Photokinesis. 



Orthopterous 



An insect in the order Orthoptera, e. g., cricket, grass- 

 hopper. 



Orthoselection 



The trend in the evolution of organisms which is in a 

 particular direction under the influence of selection, cf. 

 Orthogenesis, Natural selection. 



Ortstein 



A strongly compacted, indurated layer (Pan) of soil in 

 which the particles are cemented together with iron and or- 

 ganic matter. 



Osmoregulation 



The adjustment in the osmotic concentration of solutes 

 in fluids in organisms to environmental conditions, e. g., 

 when eels migrate from salt to fresh water. 



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