or under the canopy following cutting or after regeneration 

 operations have been started. 



Subsere 



See Secondary succession. 



Subsoil 



Approximately the B horizon in soils that have distinct 

 profiles; where the profile development is weak the subsoil 

 is below the plowed soil, or its equivalent, in which roots 

 normally grow, a vague term. 



Subsoiling 



Tillage of the Subsoil (q. v.) or the soil below the normal 

 depth of plowing, cf. Chiseling. 



Subspeciation 



The formation within a species of populations that differ 

 consistently one from another in Genotypic constitution and 

 in the resulting Phenotypes. Isolation of such Subspecies 

 may in time give rise to new Species, cf. Speciation. 



Subspecies 



A Taxon of distinct, geographically separated complexes 

 of genes, immediately below Species and above Variety (if 

 varieties are recognized in a species), sometimes considered 

 as synonymous with variety, or as an incipient species. 



Substitute Species 



See Vicariation. 



Substratum 



(1) The base, or substance upon which an organism is 

 growing. (2) A vague term for the C horizon (q. v.). 



Subtropical 



Refers to the region between the Tropics and the Tem- 

 perate zone, with distinct summer and winter seasons and 

 with greater heat than the Temperate zone. 



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