Mean sea level - A datum, or "plane of zero elevation," established by aver- 

 aging all stages of oceanic tides over a 19-year tidal cycle or "epoch." This 

 plane is corrected for curvature of the earth and is the standard reference 

 for elevations on the earth's surface. The correct term for mean sea level is 

 the National Geodetic Vertical Datum (NGVD) . 



Mesophytic - Any plant species growing where soil moisture and aeration condi- 

 tions lie between extremes. These species are typically found in habitats 

 with average moisture conditions, neither very dry nor very wet. 



Metabolic processes - The complex of Internal chemical reactions associated 

 with life-sustaining functions of an organism. 



Method - A particular procedure or set of procedures to be followed. 



Mineral soil - A soil consisting predominantly of, and having its properties 

 determined predominantly by, mineral matter usually containing less than 

 20-percent organic matter. 



Morphological adaptation - A feature of structure and form that aids in fit- 

 ting a species to its particular environment (e.g. buttressed base, adventi- 

 tious roots, aerenchymous tissue). 



Mottles - Spots or blotches of different color or shades of color interspersed 

 within the dominant color in a soil layer, usually resulting from the presence 

 of periodic reducing soil conditions. 



Muck - Highly decomposed organic material in which the original plant parts 

 are not recognizable. 



Multitrunk - A situation in which a single individual of a woody plant species 

 has several stems. 



Nonhydric soil - A soil that has developed under predominantly aerobic soil 

 conditions. These soils normally support mesophytic or xerophytic species. 



Nonwetland - Any area that has sufficiently dry conditions that indicators of 

 hydrophytic vegetation, hydric soils, and/or wetland hydrology are lacking. 

 As used in this manual, any area that is neither a wetland, a deepwater 

 aquatic habitat, nor other special aquatic site. 



Organic pan - A layer usually occurring at 12 to 30 inches below the soil sur- 

 face in coarse-textured soils, in which organic matter and aluminum (with or 

 without iron) accumulate at the point where the top of the water table most 

 often occurs. Cementing of the organic matter slightly reduces permeability 

 of this layer. 



Organic soil - A soil is classified as an organic soil when it is: (1) sat- 

 urated for prolonged periods (unless artificially drained) and has more than 

 30-percent organic matter if the mineral fraction is more than 50-percent 

 clay, or more than 20-percent organic matter if the mineral fraction has no 

 clay; or (2) never saturated with water for more than a few days and having 

 more than 3A-percent organic matter. 



A8 



