Cenozoic era which began about 12 million years ago and 

 lasted for about 1 1 million years. 



Ploidy 



Refers to the number of sets of Chromosomes in a cell, 

 e. g., Diploid, Polyploid (q. v.). 



Plot 



An area of land that is studied or used for experimental 

 purposes, in which sample areas are often located. 



Plowpan 



A compacted layer formed in the soil immediately below 

 the depth of plowing, syn. Plowsole. 



Plumule 



The portion of the embryo of a seed, above the place of 

 attachment of the cotyledons, consisting of the stem tip and 

 a few embryonic leaves. 



Pluvial 



Refers to rain. 



Pluviilignosa 



Vegetation that includes rain forest (Pluviisilvae) which 

 is dominated by evergreen broad-leaved trees, and rain bush 

 (Pluviifruticeta). 



Pneumatophore 



(1) A special structure on an aquatic or marsh plant that 

 extends above the water making a direct connection of the 

 tissues with the aerial environment. (2) Air sacs exposed to 

 the aerial environment occurring in some aquatic insects. 



Pocosin 



A bog in shallow, undrained depressions in savannas in 

 the southeastern part of the United States. 



Podzol (Podsol) 



A Zonal group of soils having surface organic layers and 



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