Perforation, vessel. - -An opening from one vessel member to another (IAWA). 



Perforation plate. --A term of convenience for the area of the wall (originally imperforate) 

 involved in the coalescence of two members of a vessel (IAWA). 



Perforation plate, scalariform. --A plate with multiple perforations elongated and parallel. 

 The remnants of the plate between the openings are called Bars (IAWA). 



Pit. --A recess in the secondary wall of a cell, together with its external closing membrane; 

 open internally to the lumen. Note: Essential components are the pit cavity and the 

 pit membrane (IAWA modif . ) . 



Pore. --A term of convenience for the cross section of a vessel or of a vascular tracheid 

 (IAWA). 



Pore, solitary. --A pore completely surrounded by other elements (IAWA). 

 Pore chain. --A series or line of adjacent solitary pores (IAWA). 



Pore multiple. --A group of two or more pores crowded together and flattened along the lines 

 of contact so as to appear as subdivisions of a single pore (IAWA). Note: The most 

 common type is a Radial pore multiple, in which the pores are in radial files with 

 flattened tangential walls between them. Another type is a Pore cluster, in which the 

 grouping is irregular. 



Protoplast. - -The mass of protoplasm enclosed by a cell wall. 



Ray. --A ribbonlike aggregate of cells formed by the cambium and extending radially in the 

 xylem and phloem (IAWA modif.). Note: The terms Medullary ray and Pith ray are 

 now restricted to the parenchyma connecting the primary cortex with the pith. 



Ray, multiseriate . --A ray two or more cells wide as seen in tangential section. 



Ray, uniseriate. --A ray one cell wide as seen in tangential section. 



Ray cell, procumbent. --A ray cell with its longest axis radial (IAWA). 



Ray cell, upright. --A ray cell with its longest dimension axial (IAWA modif.). Note: Such 

 cells compose certain uniseriate rays and parts, typically the margins, of some 

 multiseriate rays. 



Ring, annual. - -In wood and bark, a growth layer of 1 year as seen in cross section (IAWA 

 modif.), ci. Ring, growth. 



Ring, growth. - -In wood and bark a growth layer as seen in cross section (IAWA modif.). 



Spiral thickening. --Helical ridges on the inner face of, and part of, the secondary wall (IAWA). 

 Note: Often erroneously called tertiary spirals to distinguish them from the spirals of 

 primary xylem . 



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