Persistent Perianth. A perianth which remains unwithered, and often enlarged around the fruit.

Pest. Refers to any organism that damages and reduces the yield of crop or irritates or injures live stock This term is restricted to animals causing physical damage e.g., locusts.

Pesticide. Any chemical used tokill and destroy pests such asinsecticide, fungicide or herbicide.

Petal. Refers to an individual unit of corolla in angiospermic flower.

Petalody. Said of transformation of reproductive organs, stamens and carpels, into petals as taking place in double flower and flore pleno.

Petiole. Refers to the stalk that attaches the lamina of leaf to the stem with its base strengthened by widening (leaf base).

Pfitzer’s Law - That cells become progressively smaller during successive generations.

Pfluger's Rule - The mitotic figure elongates in the direction of least resistance.

Pfa - Refers to the active form of plant pigment phytochrome which possesses light absorption peak in far-red region of spectrum at about 725-730 nm. It changes to Pr reversibly and gets associated with many light mediated plant responses.

Phagocytosis - Means endocytosis which is exhibited by certain unicellular holozoic algae. In the algae protrusions of outer regions of cell formed by following movements of cytoplasm, surround the food particle, enclose it by a membrane-bound food vocuole and then lysosomes become associated with food vacuole. The intervening membrane breaks down and food particle gets digested by hydrolytic enymes.

Phanerantherous - Said of the statmens that are exerted in the flower.

Phanerogam - Refers to the plant in earlier classifications in which reproductive organs are easily visible as flowers or cones.

Phanerophyte - Refers to plant with perennating buds situated well above the ground level supported on the stem and buds are potentially exposed to environment. Such plants are found in temperate, moist region and include trees, shrubs, herbs succulents and vines. On the basis of the height of plant, these have been classified as megaphanerophytes (over 30 m), mesophanerophytes (8-30 m), microphynerophytes (2-8 m), an nanophanrophytes (below 2).

Phellem - Cork. Suberized cells which are formed in the outside regions of a stem or root, from a phellogen.

Phelloderm - A cylinder of un thickened cells formed from a phellogen on the inner side. The cells often have starch, and sometimes chloroplosts. It is a kind of secondary cortex.

Phellogen - The cork cambium. A layer of meristematic cells lying in the cortex of a stem or root. It forms cork on its outer surface, and phelloderm on the inside.

Phellandrene - A terpene which is found in Eucalyptus spp.

Phelloid - A Crust of non-suberied, or slightly suberized cells on the surface of some plants, replacing true cork.

Phenetic - Refers to the relationships between two organisms or group of organisms that are assumed on the basis of overall similarities and differences. A Phenetic classification considers as many characteristic as possible.

Phenocopy - The phenotype of a given genotype which is changed by external conditions to resemble the phenotye of a different genotype.

Phenogram - Refers to a type of dendrogram that represents the degree of phenetic similarity. It is based solely on phenetic data.

Phenology - The study of periodical phenomena in plants, e.g., the time of flowering in relation to climate.

Phenon - Refers to a cluster of groups in a phenogram that are showing phentice similarities are phenons maybe assigned rank in accordance to the level on the phenogram at which they branch off. Thus, the clusters above 80% phenon line. could be assigned the rank of genus while rank of subfamily may be assigned the rank of clusters above 55% line.

Phenon Lines - Refers to lines which are drawn at right angles to the phenogram. They show values of similarites as percentage. Greater value shows higher level of similarity.

Phenotype - The kind or type of organism that is produced by the reation of a given genotype with the environment.

Phenotypic - Caused or produced by environmental factors.

Phenoxyacetic Acids - Refer to a group of compounds some of which exhibit auxin-like activity. The substances have been found to be immune to plant's endogenous IAA oxidixing system and some such chlorine substituted forms find use as selective weedkillers. Examples are 2,4-D; 2, 4,5- T and MCP A.

Phialaspore - Said of a type of condium which is formed in many Eurotiales and Hypocreales. It is developing at the tip of specialized finger-like cells called phialides.

Phloem - Refers to the vascular tissue which conducts synthesized foods in vascular plants. It is characterised by the presence of sieve-tubes, and in some plants companion cells, fibres and parenchyma.

Phleom Fibre - An element of sclerencyma (or a strand of such elements) which is present in the phloem. It helps to support the sieve tubes.

Phloem Island - A patch of phloem which is surrounded by secondary wood.

Phloem Parenchyma - The unspecialized cells which are found in the phloem.

Phloem Ray - The part of a vascular ray that passes through the phloem.

Phosphoenolpyruvic Acid - A carbon dioxide acceptor during photosynthesis, which results in the production of pyruvic acid and phosphate.

Phosphoglyceric Acid (PGA) - The product obtained from ribulosediphoshate by reacting with carbon dioxide during the dark phase of photosynthesis. It is then reduced by NADH2. It is also an intermediate product in the anaerobic respiration of hexosediphosphate to pruvic acid.