Neutral- Refers to a material (soil, potting mixture, water, etc.) that is neither acid nor alkaline. On the pH scale, neutral has a level of 7.0. See also acid, alkaline, and pH.

Node- A point on a stem where the leaves and sideshoots arise. Nodes are often called joints and are sometimes swollen. A node may have lost its leaf.

Offset- A new plant produced naturally by an adult, usually at its base, as in bulbs, bromeliads, cacti, and some other succulents. Offsets are usually easily detached for propagation.

Offshoot- A synonym for offset.

Opposite- Refers to the placement of leaves on a stem: The leaves are borne in opposite pairs along the stem. Compare alternate.

Palmate- This word does not refer to plants commonly known as palms. It means, literally, "hand-shaped" and is applied as a descriptive term to a leaf with three or more lobes or leaflets arising from a single point of attachment on the leafstalk.

Pendent- Hanging, pendulous. The term usually describes flowers.

Perennial- A plant that lives for three seasons or more, usually indefinitely. Compare annual and biennial.

Perianth- The outer parts of the flower, consisting of the calyx and corolla, which enclose the reproductive organs.

Petal- In a flower, a separate segment of a divided corolla. Compare sepal.

Petiole- The leafstalk.

pH- Literally, the hydrogen-ion concentration in soil, potting mixture, water, etc. The pH scale is used as a means of measuring the acidity or alkalinity of any of these substances. The scale extends from 0 to 14 , with pure water (pH 7.0) as the standard. See also acid, alkaline, and neutral.

Pinching out- The removal of the growing point of a stem, thus stimulating growth from buds lower down. Its effect is to encourage bushy growth and/or flower bud production. This operation, also known as stoppinq, is usually done with the finger and thumb but it can also be carried out with a sharp knife.

Pinna- A single segment of a pinnate leaf or frond.

Pinnate- Refers to a compound leaf with two or more leaflets (pinnae) carried on each side of the midrib (rachis) in more or less opposite pairs. In some compound leaves-those of ferns in particular-each pinna is itself divided into segments (pinnules), and the whole leaf is called bipinnate. In others the secondary segments are further divided, the leaf being tripinnate or quadripinnate.

Pinnule- The smallest individual leaflet of a bi-, tre-, or quadripinnate leaf. See also pinnate.

Pistil- The female organ of a flower. The pistil normally consists of an ovary (in which the seed develops), a stigma, and a style.

Pricking out (or off)- The operation of transferring seedlings from the pots or boxes where the seeds were sown into other containers in which the seedlings can be planted individually or spaced farther apart.

Pseudobulb- Literally, a false bulb. In an epiphytic orchid the pseudobulb is a thick stem that rises from the rhizome at intervals and serves as a storage organ, not unlike an aboveground bulb that often carries the leaves and flowers, if any.

Rachis- The midrib of a compound leaf The rachis is an extension of the actual leafstalk.

Rest period- The period within each 12-month season (not necessarily a calendar year) when a plant is relatively inactive, retaining its foliage but producing little or no new growth. Compare active growth period and dormancy.

Rhizome- A fleshy stem, usually (but not always) horizontal and underground, that lasts for more than one growing season and is often a storage organ. A rhizome normally produces subterranean feeding roots as well as top growth.

Rib- Usually refers to prominent veins on a leaf, which typically project on the underside. But stems and fruits can also be ribbed. The ribs on cactus stems are frequently an especially prominent feature of the plant.

Root ball- The mass of potting mixture and roots of a plant in a pot or some other container.

Rootstock- The basal, root-carrying part of a plant on which another plant can be grafted. The term is also used to refer simply to the crown and root system as a unit; and it is sometimes loosely used as a synonym for underground rhizome.

Rosette- An arrangement of leaves radiating from a crown or distinct center, ei- ther on individual stalks (as in saintpaulias) or in an overlapping spiral (as in many of the echeverias and bromeliads).

Runner- An aboveground, more or less horizontal stem that produces buds at nodes, from which roots and new growth form. Compare stolon.

Scurf- Deposit of minute scales or particles on foliage that gives foliage a dusty, or mealy, appearance.

Seedling- A young plant soon after seed germination, still with a single, on- branched stem.

Semi-double- Refers to a flower with more than a single layer of petals, but with fewer than are found in a fully double flower.