Granular, compacted snow at the head of a glacier, or 

 similar snow elsewhere, syn. Firn. 



Niche 



(1) Ecological niche: the role of an organism in the en- 

 vironment, its activities and relationships to the biotic and 

 abiotic environment. (2) Habitat niche: the specific part 

 or smallest unit of a Habitat occupied by an organism, cf. 

 Biotope. 



Nidicolous 



Refers to young, undeveloped birds that remain in the 

 nest for a time after hatching. 



Nidifugous 



Refers to young, undeveloped birds that leave the nest 

 soon after hatching. 



Nitrification 



The oxidation of ammonia and ammonium compounds 

 to nitrites and then to nitrates by certain bacteria, cf. Nitro- 

 gen cycle. 



Nitrogen Cycle 



The circulation of nitrogen, chiefly by means of organ- 

 isms from the inorganic nitrogen in the atmosphere to ni- 

 trates, into proteins and protoplasm in plants and animals, 

 to ammonia, and return to nitrites and nitrates, cf. Nitrogen 

 fixation, Nitrification. 



Nitrogen Fixation 



The assimilation of free nitrogen of the atmosphere 

 by microorganisms in the soil or by bacteria in the nodules 

 of certain plants, especially legumes, into organic nitro- 

 genous compounds. 



Nitrophilous 



Refers to plants that grow well in soil that is rich in 

 nitrogen, e. g., many barnyard weeds. 



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