Plurilocular gametangiwn: closely arranged cluster of cells, each producing a 



gamete. 

 Polar: at the end of an axis. 



Polar nodule: the body on the inner wall at the ends of some diatoms. 

 Polygonal: with many sides. 



Pore: a hole or opening in a wall or membrane; mucilage pore; pore for en- 

 trance of antherozoid, etc. 

 Postcingular plates: sections of the wall of dinoflagellates lying between the 



median girdle and the antapical plates; posterior plates. 

 Precingular plates: sections of the wall of dinoflagellates lying between the 



median girdle and the apical plates; anterior plates. 

 Processes: extensions; lobes, arms, etc. 



Proliferate : to develop a new thallus or branches by vegetative cell division. 

 Prostrate: lying down; horizontal. 

 Protonema; Protonema stage: prostrate filaments arising from germination of 



spore, sometimes giving rise to upright branches. 

 Protophyte, Protophyta: simplest of plants; often referring to organisms with 



both plant and animal-like characteristics. 

 Protoplast : the hving material ( protoplasm ) of a cell. 

 Psammon: microorganisms inhabiting beaches or sandy shoals. 

 Pseudocilia: false cilia; hair- like extensions similar to flagella in shape but not 



used for locomotion. 

 Pseudofilament:di thread of cells incidentally arranged in a Unear series; not a 



true filament. 

 Pseudoparenchymatous: resembling a mound of cells but actually constructed 



of closely grown filaments. 

 Pseudoraphe: a false raphe (q.v. ); a clear median area in the valves of some 



diatoms which forms a line resembling a raphe. 

 Pseudopodium: a false foot; a root-like extension of protoplasm usually in- 

 volved in locomotion ( see Chrysomoeba ) . 

 Pseudovacuoles: false vacuoles; pockets of gas or mucilage in the cytoplasm 



resembling vacuoles, and usually light-refracting ( Myxophyceae ) . 

 Pulsating vacuoles: vacuoles which contract suddenly and expand slowly. 

 Pulsule: non-contracting vacuole (as in dinoflagellates). 

 Pulverulent: finely granular; powdery. 

 Pulvinate: cushion-shaped. 



Punctate: with minute points or dots; with cylindrical pores. 

 Pyramidal: in the shape of a pyramid. 

 Pyrenoid: a proteid granule which collects starch, either within a chloroplast, 



on its surface, or free within the cytoplasm. 

 Pyriform: pear-shaped, with narrow end foremost. 

 Quadrate: square; arranged to form a rectangle. 

 Quadripartition: division to form four imits. 



Raceme: a cluster of reproductive structures which mature inwardly from 

 without, the youngest structure being in the center or at the top of the 

 cluster; racemose ( adj. ) , arranged like a raceme. 

 Radial: along the radius; radiating. 



Raphe: a fissure, slit, or channel in the wall of some diatoms. 

 Rectilinear: arranged in straight rows in two directions. 

 Reniform: bean-shaped; kidney-shaped. 



Repand: referring to cells having the lateral walls concave or undulate. 

 Replicate: folded, especially the end walls of some species of Spirogyra. 

 Reservoir: posterior, enlarged portion of gullet in flagellates ( euglenoids ) . 



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