ism and usually transported to another part where it causes 

 an effect, cf. Auxin. 



Host 



An organism that furnishes food, shelter, or other bene- 

 fits to another organism of a different species, cf. Parasite, 

 Symbiont, Mutualism. 



Hudsonicm Life Zone 



One of Merriam's Life zones, includes the northern part 

 of the Boreal forest and coniferous forest on mountains 

 farther south; southern boundary delimited by the 57.2F. 

 isotherm for the six hottest weeks of the year. 



Humidity, Absolute 



The actual quantity of water vapor present in a given 

 volume of air, usually expressed in grams per cubic meter. 



Humidity, Relative 



The ratio of the actual amount of water vapor present in 

 a unit portion of the atmosphere to the quantity which would 

 be* present when saturated, cf. Psychrometer, Hygrometer. 



Humification 



The process of decay of organic material to Humus. 



Humus 



(1) Organic matter in a more or less stable advanced 

 stage of decomposition, dark in color, with a high nitrogen 

 content, a carbon-nitrogen ratio near 10:1, and other chemi- 

 cal and physical properties such as a high Base exchange 

 capacity, water absorption, and swelling. (2) Residues in the 

 soil of plants and animals that have undergone an appreci- 

 able degree of decomposition. 



Humus, Raw 



See M or. 



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