26 



MISC. PUBLICATION 110, U. S. DEPT. OF AGBICULTUEE 



Perennial: Lasting for three or more 

 years ; said especially of herbaceous 

 plants that are neither annual nor 

 biennial. A perennial plant. Fre- 

 quently expressed by the symbol % . 



Perfect: Having both stamens and pis- 

 til (s) ; said of flowers. The great 

 majority of flowers are perfect. 



Perfoliate: Literally through the leaf; 

 refers to leaves or stipules whose 

 clasping bases are united beyond, 

 and as if pierced by, the stem. 

 (Fig. 53.) 



Perianth: The floral envelope, consist- 

 ing of the calyx and corolla, how- 

 ever incomplete or modified. Used 

 particularly for plants, like lilies, in 

 which the calyx and corolla can not 

 readily be distinguished. 



Figure 53. — Perfoli- 

 ate leaf, as in thor- 

 oughwort spring- 

 beauty (Claytonia 

 perfoliate*) 



Pericarp: The outer covering, varying 

 greatly in texture and thickness, of 

 a fruit and corresponding to the 

 outer walls of the ovary from which 

 it was fashioned. In a pod the peri- 

 carp is mostly thin and dry; in a 

 drupe or berry, thick and fleshy ; in 

 a nut, bonelike in texture. The 

 pericarp often consists of two lay- 

 ers (endocarp and exocarp) or of 

 three layers (endocarp, mesocarp, 

 and epicarp). In a peach or plum, 

 for instance, the bony stone sur- 

 rounding the seed is the endocarp, 

 the edible fleshy portion is the meso- 

 carp, or sarcocarp, while the thin 

 outermost rind, or peel, is the epi- 

 carp. 



Perigynium (pi. -ia) : The saclike 

 organ which completely incloses the 

 ovary, and at maturity the achene 

 (seed), in sedges of the genus 

 Carex; the perigynium is usually 



Figure 54. — Pistil- 

 late (female) floral 

 parts of a sedge 

 {Carex festivellaj: 

 A, Perigynium ; B, 

 scale, which sub- 

 tends A 



more or less beaked and often 2- 

 toothed at apex and affords some 

 of the best characters for distin- 

 g u i s h i n g 

 species of this 

 difficult genus. 

 (Fig. 54, A.) 



Perigynous: Sit- 

 uated around 

 the ovary ; said 

 of petals and 

 stamens when 

 borne on the 

 calyx, as, for 

 example, in the 

 rose family 

 (Rosa cese). 

 Literally, 



around (the) woman, i. e., encircling 

 the pistil. 



Persistent: Remaining attached, in- 

 stead of falling away, at the time 

 such parts ordinarily drop off; said 

 of evergreen leaves, calyces remain- 

 ing at fruiting time, etc. 



Petal: Typically one of the separate, 

 usually colored, modified leaves of a 

 choripetalous corolla and making up 

 the inner and upper series of the 

 floral envelope (perianth) parts. 

 Also, though less precisely, one of 

 the more or less fused divisions of 

 a gamopetalous corolla (as the five 

 united petals of a manzanita co- 

 rolla). 



Petaloid: Petallike, as the petaloid in- 

 volucral bracts of the flowering dog- 

 woods (Cornus florida and C. nut- 

 tallii). 



Petiolate: Furnished with a petiole, or 

 leafstalk (said of leaves). 



Petiole : A leafstalk, whereby the blade 

 of a leaf is attached to the plant 

 stem. 



Petiolulate: Furnished with a petiolule 

 (said of leaflets). 



Petiolule: The stalk of a leaflet, corre- 

 sponding to the petiole of a leaf. 



Phanerogam: A flowering, seed-produc- 

 ing plant; a seed plant (spermato- 

 phyte) as distinguished from a 

 cryptogam. The higher of the two 

 main divisions, or subkingdoms, into 

 which the vegetable kingdom is di- 

 vided ; in turn separated into angio- 

 sperms and gymnosperms. 



Phloem: Soft bast or sieve tissue in 

 plants. The outer of the two com- 

 ponent parts of fibrovascular bun- 

 dles. Phloem consists of sieve tubes 

 with the accompanying cells and 

 parenchyma. 



Photosynthesis: The complex process 

 by which starch (CeHwOs) is manu- 

 factured by the chloroplasts, or 



