mediacy of Hybrids into another species, resulting in the 

 genetic modification of the latter. 



Invasion 



The Migration (q. v.) and Establishment (q. v.) of an 

 organism in a new location. 



Inverse Stratification 



The condition in which the water just beneath the ice 

 in a body of water is near the freezing temperature and 

 within a short distance below shows a rapid rise to 3C., 

 and further below a gradual increase to 4C., or to the 

 maximum temperature of the lake or pond. cf. Thermal 

 stratification. 



Inversion, Temperature 



An increase in air temperature with an increase of alti- 

 tude, instead of the normal decrease. 



Invertebrate 



An animal lacking a spinal column, e.g., insects. 



In Vitro 



Refers to experiments on cells, etc., which are carried 

 on when they are separated from the living organisms, e.g., 

 tissue cultures, cf. In vivo. 



In Vivo 



Refers to location within the living system, cf. In vitro. 



Involucre 



A number of closely associated bracts subtending a flower 

 or flower cluster. 



Involution 



(1) The diminution in the size of an organ, cf. Hyper- 

 plasy, Hypertrophy. (2) The formation of abnormal yeasts, 

 bacteria, etc. 



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