Palisade Stereide - A rod-shaped cell occurring in the testa of a seed. It is thick walled, elongated, and lies at right-angles to the surface of the seed.

Palisade Tissue - One or more layers of palisade cells beneath the epidermis of a leaf.

Palmate - Having several (5-7) lobes, segments etc., spreading from the same point, like the fingers of a hand. The term is especially applicable to leaves.

Palmelloid - A multicellular growth form in which body of organism is composed of large number of loosely aggregated cells which are held together in a mucilaginous matrix. Such forms are characteristic of certain blue green large.

Palynology - Study of fossil spores, pollens and similar structures

Pampas - A term for South American grassland.

Pangenesis - Refers to the theory which postulated that the heredity of organisms is determined by the summation of influences from an indefinite number of particles (pangenes) derived from all parts of the body-tissues and variably affected by variation in the environment.

Panicle (1) A branched raceme, in which each branch is bearing a raceme of flowers.
(2) More generally any branched inflorescence which is in any way complex.

Panmixis - Said of the unrestricted random crossing, which is probably quite rare but may be applicable to crossing that appears random with respect to a particular character.

Pancolpate - A pollen that is having many colpi.

Panphotometric - Said of a narrow leaf which stands nearly or quite.

Pantonematic Flagellum - A flagellum which has mastigonemes on both sides of the main axis.

Pantothenic Acid - A part of co-enzyme, A, and one of the B group of vitamins.It is essential for the growth of yeasts and some bacteria.
CH3 OH
HOCH2 -6- 6H-CONH-CH2-CH2-COQH
I CH3

Papain - A enzyme (or group of enzymes) occurring in paw-paw leaves. In neutral solution, it hydrolyses protein to polypeptides.

Papilla - Refers to a projection from a cell, usuallly from epidermal cell. It is usually regarded as a kind of trichome, often swollen and covered with wax and in xerophytes serves as protection from strong sunlight and water loss.

Pappus - A ring of fine, sometimes feather, hairs, developed from the calyx, and covering the fruit (usually of the Compositae). It acts as a parachute, and helps in wind dispersal.

Parachute Disseminule - A fruit or seed having hairs, or some other mechanism which helps in dispersal by wind.

Paraflagellar Body - Said of the light-sensitive structure which is visible as a swelling on the flagellum of some members of Euglenophyta.

Parallel Evolution (parallelism). Refers to the evolution of similar adaptations in related organisms taking place due to being subjected to similar selection pressure even when distributed in widely separated regions.

Parallelodromous - Said of the form of leaf venation in which two or more primary veins a originally at the base of lamina and running to the apex in an essentially parallel manner as in many monocotyledonous leaves. The usual term for such venation is parallel.

Paramylum - A polysaccharide forming in both green and colourless algae of Euglenophyta as storage product.

Paraphyletic - Said of a group of organisms that are not all descendents of a common ancestor.

Paraphyll, Paraphylum - A leaf-like, or filamentous appendage near a 'leaf' in mosses.

Paraphysis - A sterile hair which is growing around, or among reproductive structures and is found in some algae, ascomycetes, basidiomycetes and mosses.

Paraphysoid - A plate of cells occurring between the asci in as comycetes.

'Paraplasm - Said of the inactive vegetative part of the protoplasm.

ParasexUal Recombination. Said of the type of recombination which is occurrir1g in progeny of certain heteroaryotic fungi in which meiotic segregation does not take place. The sequence of events involved is called parasexual cycle.

Parasite - A plant or animal that is living on, or 1n another organisJ1l, called the host. The parasite extracts food from the host, aI1dlives at the 1atter'sdetriment.

Parasitic Castration - The condition when a plant is unable to produce fruit due to damage to the reproductive organs by a parasite.

Parasitism - Said of the temporary or permanent relationship existing between two different organisms in which oneorganism is benefited and is called parasite while other partner is harmed and is called host.

Parasporangium - A sporangium having paraspores.

Parasote - A spore which is produced on the tetrasoprophyte of some Rhodophyta. It is very likely to be diploid, and always germinates to produce a new tetrasporophyte.

Parastichy - A spiral line which is passing once around a stem through the bases of successive leaves.

Parasymbiosis. Refers to the condition when two organisms grow together with out assisting or harming one another.

Parasynapsis, Parasyndeis - Said of the side-by-side association of a pair of chromosome as in zygotene and pachytene.

Parathecium - A layer of hyphae present around the apothecium of a lichen or Discomycete.

Paratonic - Said of a plan. movement which is induced by external stimulus.

Parenchyma - Refers to a tissue of undifferentiated cells, which are more or less spherical, frequently unspecialized, and with cellulose cell-walls. Air spaces are often present, and the tissue is often for storage.

Parichnos - In certain lower vascular plants, a pair of scars, one on each side of the leaf base; each scar is marking the end of a strand of parenchyma which is passing into the stem.

Parietal Placentation - Refers to a type of placentation in which placentae are developed along the fused margins of carpels in a unilocular, compound ovary.

Paripinnate - Said of a pinnate leaf in which all the leaflets are paired as in Vida.

Parthenoapogamy. The fusion of vegetative nuclei.

Parthenocarpy. The development of a fruit without involving the formation of seeds as a result of (a) lack of pollination, (b) lack of fertilization, (c) lack of embryo development. The condition can be artificially induced by application of hormones.

Parthenogamy. The union of two female gametes, or the structures equivalent to them.

Parthenogenesis - Said of the development of an egg cell into embryo without involving fertilization, usually due to defective meiosis that results in egg nucleus having unreduced number of chromosomes e.g., in Taraxacum. In some species e.g., Hieracium, any cell of nucellus other than the memgaspore may be involved in parthenogenesis.

Parthenospore (azygopore) - A thick-walled resting spore produced from unfertilized female gamete by involving parthenogesis in certain algae e.g., Protosiphon and fungi e.g., Entomophthora muscae.

Partial Habitat - The habitat occupiedby a plant during one stage of its life-cycle.