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GLOSSARY 



Passage cells, the thin-walled endoder- 

 mal cells which commonly lie on the 

 same radii as the protoxylem strands. 



Pectinate, (of a vascular system) ap- 

 plied where two series of vascular 

 bundles alternate with each other 

 as the teeth of two combs. 



Pedicel, the supporting axis of a single 

 flower. 



Peduncle, the supporting axis of a 

 single flower or a flower cluster. 



Pentacyclic, (of flower) with five 

 whorls of floral parts. 



Pentamerous, with parts in fives, as a 

 calyx of five sepals. 



Pentarch, (of root) a stele with five 

 protoxylem groups. 



Pepo, a fruit developed from an epigy- 

 nous flower in which the tissue of the 

 receptacle surrounds the pericarp, 

 forming a more or less hardened rind 

 as in cucurbits. 



Perennial, with a life cycle of more 

 than two years' duration. 



Perfect, (of flower) having both sta- 

 mens and carpels. 



Perianth, the floral envelope comprised 

 of the calyx and corolla (if present) 

 regardless of their form. 



Periblem, the layer or histogen from 

 which the cortex is derived. 



Pericarp, the mature ovary wall. 



Periclinal, curved in the same direc- 

 tion as the surface or circumference; 

 (of walls) those which are parallel 

 with the surface. 



Pericycle, the outermost cell-layer of 

 the stele lying adjacent to the endo- 

 dermis, frequently becoming a multi- 

 layered zone. 



Periderm, the outer protective layer 

 in older axes, consisting of the phel- 

 logen and its derivative tissues, 

 phellem and phelloderm. 



Perigynous, (of flowers) applied when 

 there is conjoint growth of the outer 

 cycles of floral parts distinct from the 



carpel or carpels and divergent below 



them. 

 Peripheral, on or near the margin. 

 Petal, one of the members of the 



corolla. 

 Petiole, the supporting stalk of a leaf. 

 Phellem, cork tissue. 

 Phelloderm, cells cut off centripetally 



by the phellogen. 

 Phellogen, a lateral meristem that cuts 



off phelloderm and phellem; the cork 



cambium. 

 Phloem, a complex vascular tissue 



which may include sieve tubes, com- 

 panion cells, fibers, parenchyma, and 



secretory cells. 

 Phyllotaxy, the mode in which leaves 



are arranged on the stem axis. 

 Phylogeny, the developmental history 



of a race rather than an individual. 



Cf. Ontogeny. 

 Pistil, a carpel or group of undiverged 



carpels, commonly subdivided into 



stigma, style, and ovary. 

 Pith, the central parenchymatous por- 

 tion of the axis; the medulla. 

 Placenta, the surface in an ovary that 



bears the ovules. 

 Plasmodesma, delicate threads or fibrils 



of cytoplasm that pass through the 



walls of adjacent cells, establishing 



protoplasmic continuity. 

 Plastid, a specialized body occurring 



in the cytoplasm of a cell which may 



be colorless or pigmented. Cf. Leuco- 



plasf, Chloroplast. 

 Plerome, the layer or histogen from 



which the stele is derived. 

 Plumule, the bud or growing point of 



the embryo. 

 Pod, a dry, many-seeded, dehiscent 



fruit; a legume, silique, etc. 

 Polyarch, (of root) a stele with several 



to many protoxylem groups. 

 Pome, a fleshy fruit developed from an 



epigynous flower in which the inner 



portions of the carpel wall are some- 



