Normal Erosion 



The Erosion that occurs on land under natural environ- 

 mental conditions not disturbed by human activities, cf. 

 Accelerated erosion. 



Normal Spectrum 



See Biological spectrum. 



Norther (Norte in Central America) 



A northerly wind, especially a strong one, that begins 

 suddenly during the colder half of the year in the region 

 from Texas southward, including the Gulf of Mexico and 

 the western Caribbean. 



Notogea 



One of the three continental fauna! realms. It includes 

 the Australian region (q. v.). cf. Megagea, Neogea. 



Nuciferous 



Refers to nut-bearing plants. 



Nunatak 



A body of land, such as a mountain, projecting at some 

 time above a mass of ice and snow, or above a glacier. 



Nurse Crop 



See Companion crop. 



Nutation 



A circular or spiral movement of the growing portions 

 of plants such as stems or tendrils. 



Nutrient (Plant) 



Any substance absorbed by a plant that is used in its 

 Metabolism. 



Nyctinasty 



The movement of a plant organ in response to alterna- 

 tion of night and day as in clover leaflets. 



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