Nivation 



A kind of erosion caused by the action of snow, e. g. 

 Solifluction. 



Nocturnal 



Refers to night time. cf. Crepuscular, Diel, Diurnal. 



Nodule 



A structure formed on the roots of most legumes and a 

 few other species containing bacteria that carry on Nitrogen 

 Fixation. 



Nodum 



An abstract unit of vegetation such as Association, Socia- 

 tion, and Alliance; corresponds to Taxon in Systematic*. 



Nomad 



A member of a group, especially of primitive people, who 

 change their dwelling place frequently. 



Nomina Conservanda 



Names of organisms whose usage is maintained by agree- 

 ment of systematists although the names may be contrary to 

 the rules of nomenclature. 



Non-available Water 



The amount of water in the soil when a plant wilts 

 permanently, cf. Wilting. 



Non-reactive Factor 



An environmental factor such as weather conditions 

 which are not influenced by the density of individuals in a 

 population, but may produce increasingly adverse effects 

 with increasing density, cf. Density-independent factor, Den- 

 sity-dependent factor. 



Normal Dispersion, Normal Distribution 



The distribution in an area of individuals of a popula- 

 tion that is at random. 



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