Outer fissure: the upper part of the raphe (q.v. ) in pennate (bilaterally sym- 

 metrical) diatoms. 



Packet: compact cluster or aggregate of cells, often cubical. 



Palmella stage: a condition resembling Palmella, in which a motile cell has 

 lost organs of locomotion, become quiescent, and undergone division to 

 form clumps of daughter cells encased in mucilage. 



Palmelloid: similar to Palmella; forming clumps of mucilage-encased cells. 



Panduriform: fiddle-shaped; an elongate figure, broadest at the anterior end 

 and with concave lateral margins. 



Papilla (Papillose): a small nipple-like swelling (adj.: bearing papillae). 



Paramylon: a solid carbohydrate food reserve formed by certain euglenoids. 



Parenchymatous: cushion-like; composed of a mound of cells. 



Parietal: lying along the wall; peripheral in the cell. 



Parthenospore: a zygote-like spore produced from a single gamete which de- 

 velops a thick wall. 



Patent oogonium: oogonium (in Bulbochaete) borne on a division of the 

 suffultory cell (q.v.) that has been cut off obUquely from the lower ceU 

 rather than by a transverse wall; free; free spreading. 



Pectin, Pectose: gelatinous substance (carbohydrate) found in the wall of 

 many algae. 



Pedicel: a stalk or stem, often delicate and short. 



Pelagic: floating organisms, especially in the ocean; surface organisms. 



Pellicle: a thin membrane or sheet. 



Pellucid: translucent, clear. 



Penicillate: brush-like. 



Pennatae: diatoms which are bilaterally symmetrical. 



Pericentral cell: a cell (one of several) inclosing a central cell or filament. 



Peridinin: a reddish pigment found in some dinoflagellates. 



Periphyton: organisms attached at the water level to aquatic plants. 



Periplast: the bounding membrane, especially the cell membrane of euglenoids. 



pH: relative amount of free hydrogen ions; indicator of acidity or alkalinity. 



Pharyngeal rods: bodies lying parallel with the gullet (e.g., Peranema) . 



Phototactic: movement or orientation with respect to light stimulus. 



Phycochrysin: brown pigment found in Chrysophyceae ( chrysochrome ) . 



Phycocyanin: a blue pigment in solution in cells of Myxophyceae and some 

 Rhodophyceae. 



Phycoerythrin: red pigment in Rhodophyceae and some Myxophyceae. 



Phycopyrin: brownish-red pigment in some dinoflagellates. 



Phylogeny: racial development: racial history. 



Pigment-spot: See eye-spot. 



Piliferous, Pilose: hairy. 



Placoderm desmid: desmid usually constricted in the midregion, with wall in 

 two sections. 



Plakea: plate of cells formed by successive divisions from mother cell. 



Plane: smooth and even, not folded. 



Planoconvex: with convex surface opposite a flat surface. 



Planogamic heterogamy: condition of having gametes of different size, motile 

 and non-motile. 



Plankton (Planktonic) : floating organisms unable to swim against currents, 

 drifting. 



Plasmodium: naked protoplasm as in slime molds. 



Plastid: any one of several kinds of bodies in the cytoplasm of a cell. 



Plicate: folded. 



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