Aril 



A special covering on a seed, arising from base of the 

 ovule or the stalk, sometimes pulpy or brightly colored as 

 in the bittersweet. 



Arrhythmic 



Refers to the activity of an organism which occurs during 

 both day and night, cf. Diurnal, Nocturnal. 



Arroyo 



A stream channel or gully in an arid country, usually 

 with steep banks, dry much of the time. 



Arthropod 



An animal in the phylum Arthropoda such as insects, 

 crabs, spiders, centipedes. 



Artifact 



(1) A substance or appearance of a specimen of an organ- 

 ism or preparation of part of an organism which is not 

 present in the living tissue. (2) Something made by man 

 especially primitive man. 



Artificial Selection 



Selection by man of plants or animals which possess 

 desired qualities for reproduction and for the improvement 

 of the properties of the organisms, cf. Natural selection. 



Artificial Stocking 



The introduction of animals from another region, or the 

 artificial propagation of animals, into an area, e.g., stocking 

 streams with fish or introducing quail into an area where 

 they are scarce or lacking. 



Asexual Reproduction 



Reproduction of organisms without the fusion of gametes, 

 cf. Apomixis. 



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