Rasorial 



Refers to an animal that usually scratches the ground 

 for food, e.g., barnyard fowl. 



Rassenkreis 



A series of races in which distinct forms of a Polytypic 

 species replace each other in a geographic progression, cf. 

 Race (1). 



Ratoon 



A shoot from a perennial plant such as sugarcane. 



Raunkider's Law of Frequency 



See Frequency, law of. 



Raunkider's Life-form Classification 



A system of classification of Life-forms of plants based on 

 the kinds and position of the organ with respect to the soil 

 level that survives unfavorable environmental periods, cf. 

 Phanerophyte, Geophyte. 



Rdvine 



An elongated, narrow depression, larger than a gully, 

 usually formed by running water. 



Rdw Humus 



See Mor. 



Reaction 



(1) The effects which one or more organisms produces 

 upon its habitat, cf. Interaction. (2) The degree of acidity or 

 alkalinity of a substance, usually expressed as pH (q. v.). cf. 

 Hydrogen-ion concentration. 



Reaction Time 



The time required by an organism for the manifestation 

 of a response to a stimulus. 



Realm 



One of the major divisions in the classification of con- 



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